Lakhmir Singh Manjit Kaur Biology 2020 2021 for Class 10 Science Chapter 8 - Model Test Paper 1

Answer:

When metals reacts with water(Hot, cold or steam), they displace hydrogen from the water and Hydrogen gas is released. Metals react with water according to their reactivities. Only those metals react with water, which are above hydrogen in the reactivity series. 

(a) Out of given metals, only magnesium reacts with hot boling water and forms magnesium hydroxide and hydrogen gas.

(b) Out of all the given metals only copper is less reactive than hydrogen, so it cannot displace hydrogen from the water even if the temperature is so high. That's why copper does not react even with the steam.

Answer:

In the space, there is no atmosphere. So, the sunlight does not scatter in the space. Hence, an astronaut sees the dark sky.

Answer:

Refractive of water is more than the air, so the speed of the light decreases when it travels from the air into the water. That's why when light rays travel into the water, they bend towards the normal. Hence, the part of the pencil dipped inside water appears to be bent at the water surface, as shown in the above figure.

Answer:

The reaction which involves gain of oxygen, loss of hydrogen or loss of electrons is defined as the oxidation reaction.



(a) In the given reaction, C is gaining oxygen, so it is oxidized.
(b) Whereas zinc(Zn) is losing oxygen, so it is reduced.



 

Answer:

Reproduction is the process by which an organism gives rise to a new organism/offspring.
DNA copying is more commonly known as DNA replication. It is an important process which ensures that equal amount of DNA (genetic material) is passed on to the new cell as the parent cell multiplies.

Answer:

Physical and chemical properties used by Mendeleev in creating his periodic table:

1. Physical properties: Mendeleev arranged the periodic table in the increasing order of the atomic masses of the elements.

2. Chemical properties: Mendeleev distributed the elements into groups on the basis of formation of hydrides and oxides.

Challenges to Mendeleev's periodic law:

(i)  Position of the isotopes: Isotopes have different masses, so they must be assigned separate positions in the periodic table.
(ii) Different groups of similar elements: Some chemically similar elements are placed in different groups, while some chemically different elements are placed in the same group.

Answer:

(a)  Formation of sodium chloride by electron transfer:

Electronic arrangement of sodium and chlorine:
 

Formation of ionic bond:


(b) Sodium chloride has a high melting point because of strong lattice structure formed due to the ionic bond. Interatomic attractive forces hold the two elements tightly and increase their boiling point.

(c) In the electrolytic refining of impure copper metal, the impure copper plates act as the anode while a thin sheet of pure copper act as the cathode.

Answer:

(a) When quicklime or calcium oxide(CaO) is added to water then it reacts vigorously with water and forms slaked lime or calcium hydroxide(Ca(OH)₂). This reaction is highly exothermic and a large amount of heat is released in the process. The chemical reaction involved is as follows: 

$\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Ca}\left(\mathrm{OH}{)}_2\right(\mathrm{aq})$

(b) Baking powder is a mixture of baking soda(sodium hydrogen carbonate) and a solid, edible acid such as tartaric acid or citric acid. When baking powder is mixed with water, the sodium bicarbonate reacts with tartaric acid to produce carbon dioxide gas. The carbon dioxide gas gets trapped in the wet dough made for baking a cake or bread and then bubbles out slowly. Which makes the cake or bread soft and spongy.

Answer:

(a) Refractive index of a medium is the measure of the speed of light in that, medium with respect to the vacuum. It is defined as the ratio of the speed of the light in a vacuum to the speed of the light in the given medium. So, the term "The refractive index of diamond is 2.42" means that the speed of light in diamond is $\frac{1}{2.42}$ times the speed of the light in vacuum.

(b) We can put a magnetic compass nearby a bar magnet. The needle of the compass will show deflection in the direction of magnetic field lines. If we move the compass around the magnet, we can get the exact path of magnetic field lines around the bar magnet. 

Answer:

(a) All the resistors are connected in parallel. They are getting an equal voltage across their ends, which is equal to the voltage of the battery.

Hence, the current flowing through each resistor = $\frac{\mathrm{Voltage} \mathrm{across} \mathrm{the} \mathrm{battery}}{\mathrm{Resistance} \mathrm{of} \mathrm{the} \mathrm{resistor}}$

The voltage across the battery = 6 V

Current flowing through 5-ohm resistor = $\frac{6 \mathrm{V}}{5 \mathrm{\Omega }}=1.2 \mathrm{A}$


Current flowing through 10-ohm resistor = $\frac{6 \mathrm{V}}{10 \mathrm{\Omega }}=0.6 \mathrm{A}$

Current flowing through 30-ohm resistor = $\frac{6 \mathrm{V}}{30 \mathrm{\Omega }}=0.2 \mathrm{A}$

(b) The total current in the circuit = Sum of the current through all the resistors = 1.2 A + 0.6 A + 0.2 A = 2 A

(c)The total resistance of the circuit$=\frac{\mathrm{Total} \mathrm{voltage}}{\mathrm{Total} \mathrm{current}}=\frac{6 \mathrm{V}}{2 \mathrm{A}}=3 \mathrm{\Omega }$
 

Answer:

(a) A diagram to show the formation of an image of a distant object by a myopic eye is shown below:



The defect of a myopic eye can be corrected by using a concave lens. A concave lens helps in diverging the rays to form an image on the retina of the eye.

(b) Causes of myopia: (i) Elongation of the eyeball (ii) Decrease in the focal length of the eye lens.

(c) As it is a case of myopia one has to use a concave lens.
The far point is 1.5 m, it means that the image should be formed at 150 cm or before on the same side as the object. The distance of the object is taken as infinite, as the problem is nearsightedness.

Now, u = ∞, v = –150 cm and f = ?

Using the lens formula, $\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

$$\begin{gathered} \Rightarrow \frac{1}{-150}-\frac{1}{\infty }=\frac{1}{f} \\ \Rightarrow \frac{1}{f}=\frac{1}{-150} \\ \Rightarrow f=-150 \mathrm{cm} \end{gathered}$$

The maximum focal length to be used = $-150 \mathrm{cm}$

Hence, the power of the lens required = $P = \frac{1}{f( \mathrm{in} \mathrm{meter})}=\frac{1}{1.5 \mathrm{m}}=0.67 \mathrm{D}$

Therefore, a concave lens with power 0.67 D or more is required for the correction in vision.

Answer:

(a) Overloading: When too many electrical appliances of high power voltage are switched on at the same time, a large current from the circuit is drawn. This is called overloading of the circuit. Overloading also occurs due to accidental hike in the supply voltage.

Shortcircuiting: When the live wire and neutral wire come into direct contact, a large amount of current flows through the circuit due to very small resistance, this is called short circuiting. The heat produced during short-circuiting is so high that it may cause a fire.

(b) The coil of the electric toaster is made up of an alloy because alloys have better properties than the pure metals. Such as,

1.  They have a high melting point. This is necessary for the electric toaster as it is a heating device.
2.  More resistant to oxidation. This is another requirement in a toaster.
3.  Mechanically stronger than that of pure metal.

Answer:

“Damage to the ozone is a cause of concern”; this is because ozone depletion has created a hole in the ozone layer over the Arctic region.

Damage in the ozone layer allows the harmful UV rays to reach the earth surface. UV rays can cause -

• skin cancer, ageing and corneal cataracts in human beings
• death of many phytoplanktons leading to the increase in the rate of global warming
• increase in the global warming rate, in turn, leads to the melting of Arctic ice cap which may further result in the increase in sea level

• Not buying products in aerosol cans and maintaining air-conditioning filters and units. In order to halt the depletion of the ozone layer, countries around the world have banned the use of chlorofluorocarbons and other ozone-depleting substances. These compounds produce chlorine and bromine atoms which reach the atmosphere react with ozone, thus destroying it. 
• By minimising the use of vehicles to limit the emission of harmful gases which cause damage to the ozone layer.

Answer:

Hormones are intercellular chemical messengers secreted by specific endocrine glands of the body. They travel throughout the body to reach the target organs or cells and initiate a process. Chemically, hormones are proteins. Once the hormone is secreted from the gland, it is directly poured into the blood stream, which transports it to the site of action. They maintain the balance of biological activities in the body.

The hormone secreted by thyroid gland is thyroxine hormone. It regulates carbohydrate, fat, and protein metabolism in the body. 

It is advised to use iodised salt because iodine is required for the synthesis of thyroxine hormone. Deficiency of iodine would result in deficiency of thyroxine hormone and in turn lead to a disease called goitre.

Answer:

(a) 

Answer:

(a) The electronic configuration of carbon is 2, 4.  The electron present in its outer most shell is 4 but for the stability, the number of electrons has to be 8. So, carbon can neither lose 4 electrons nor gain 4 electrons to complete its octet. For losing or gaining electrons from the outer-most shell, we require an enormous amount of heat/energy, which is not possible in nature. Hence, the four electrons present in the outer-most shell will try to share with other four electrons in order to fulfill their octet. That is why it forms covalent bonds.

(b) Two of the main reasons because of which carbon forms a large number of organic compounds are:
1. Tetravalent nature of carbon.
2. Greater C-C bond strength.

(c) Organic compound "X" freezes in colder countries must be a carboxylic acid containing molecule. So, the molecular formula will be CH₃COOH.
When a carboxylic acid is treated with alcohol in the presence of sulphuric acid, it gives a sweet-smelling compound ester. So, when ethanoic acid treated with ethanol, it will give ethyl ethanoate.
Hence, X will be ethanoic acid and Y will be ethyl ethanoate which is a sweet smelling compound.

(ii) The reaction involved is as follows: 
$\underset{\mathrm{Ethanoic} \mathrm{acid}}{{\mathrm{CH}}_3\mathrm{COOH}}+\underset{\mathrm{Ethyl} \mathrm{aclochol}}{{\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}}\stackrel{{\mathrm{H}}_2{\mathrm{SO}}_4}{\to }\underset{\mathrm{Ethyl} \mathrm{ethanoate}}{{\mathrm{CH}}_3{\mathrm{COOCH}}_2{\mathrm{CH}}_3}+{\mathrm{H}}_2\mathrm{O}$

 

Answer:

(a) A homologous series is a series of organic compounds, which differ by a same repeating unit and have similar chemical properties due to the presence of the same functional group. 

Characteristics of homologous series:
(i) Two consecutive members of a homologous series differ by a (-CH₂) unit and a mass of 14 amu. 
(ii) Homologs of a series have similar chemical properties.

(b) (i) When 5% alkaline potassium permanganate is added to warm ethanol, ethanol gets oxidize to form ethanoic acid.

${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}\stackrel{\mathrm{alk}.{\mathrm{KMnO}}_4}{\to }{\mathrm{CH}}_3\mathrm{COOH}$

(ii) The compound formed during the reaction is ethanoic acid.

(c) Carboxylic acids react with sodium bicarbonate to produce brisk effervescence due to the release of carbon dioxide gas, whereas alcohols do not react with sodium bicarbonate.

Answer:

(a) It means that the 1 joule of energy is used up in transferring a charge of 1-coulomb between two points. A voltmeter is used to measure the potential difference across a conductor and it is always connected in parallel.

(b) The heating element of the heater is made up of an alloy which has very high resistance. So, when current flows through the heating element, it becomes too hot and glows red due to the heating effect of current. But the resistance of cord which is usually of copper or aluminium is very low so it does not glow.  

(c) The conductivity of a material is indirectly proportional to its resistivity.
(i) Out of silver and copper, silver has less resistivity, that's why it is a good conductor as compared to copper. 
(ii) The material used in electrical heating devices must have high resistance. So, a material with high resistivity should be used from the table. Nichrome has the highest resistivity, it would have the highest resistance among all the given materials. Hence, it should be used for electrical heating devices. 

 

Answer:

(a) An ammeter is used to measure the current in a circuit. Unit of electric current is ampere. 

(b) (i) Variable resistance or Rheostat (ii) A closed switch

(c) (i)


(ii) $\frac{V}{I}$ for 0.8 V, 1.2 V and 1.6 V is the same as the graph between the voltage and the current is a straight line. So, the $\frac{V}{I}$ ratio is constant for all the values of current and voltage.

Answer:

Ans 20. (a)
 
(b) (i) Liver −It is the largest gland in the digestive system. It secretes bile, which helps in the digestion of fats into fatty acids and glycerol.

(ii) Pancreas − It secretes enzymes, such as trypsin and lipase for the digestion of proteins and fats respectively.

(c) (i) Absorption of digested food - small intestine
(ii) Absorption of water - large intestine

Answer:

(a)

(b) (i) Functions of blood -

• transports hormones and nutrients throughout the body
• transports oxygen to cells and removes carbon dioxide
• maintains the body temperature

(ii) Functions of lymph -

• contains lymphocytes that are involved in immune response
• carries nutrients, hormones, etc.
• absorbs fats in lacteals (found in intestinal villi)

Answer:

When a metal(M) is treated with dilute sulphuric acid, metal will displace hydrogen and form metal sulphate, along with colourless and odourless hydrogen gas. Hydrogen gas produced in the reaction will evolve with bubbles.

$\mathrm{M}+{\mathrm{H}}_2{\mathrm{SO}}_4\to {\mathrm{MSO}}_4+{\mathrm{H}}_2$

(a) Hydrogen gas will evolve.

(b) The method of collection of the gas shown in the figure is known as "downward displacement of water".

(c) Hydrogen gas is insoluble in water.

(d) Hydrogen gas is lighter than air.

Answer:

(a) When Ashwini adds acetic acid in the universal indicator, he will observe a colour either orange or yellow, depending upon the concentration of acetic acid. Because acetic acid is a weak acid, having a pH range of 3-6, so it will change the colour of universal indicator to orange or yellow.

(b) When Ashwini adds acetic acid in distilled water, he will observe acid and water mix uniformly.

(c) When Ashwini adds acetic acid in the sodium hydrogen carbonate, he will observe effervescence due to the formation of carbon dioxide.

${\mathrm{CH}}_3\mathrm{COOH}+{\mathrm{NaHCO}}_3\to {\mathrm{CH}}_3\mathrm{COONa}+{\mathrm{CO}}_2+{\mathrm{H}}_2\mathrm{O}$

(b) When Ashwini adds acetic acid in the phenolphthalein, he will observe the pink colour of phenolphthalein changes to colourless, because phenolphthalein turns colourless in acids.
 

Answer:

White light gets split up into seven colors, which are as follows:

(7) Violet (6) Indigo (5) Blue (4) Green (3) Yellow (2) Orange (1) Red

(a) Potassium permanganate is an odorless dark purple colored solid. Hence, color position 7 corresponds to potassium permanganate closely. 

(b) The red color is a mark of danger or symbol for danger in general. Hence, color position 1 suits closely for danger signal. 
 

Answer:

(a) More heat will be obtained when the heating elements are connected in parallel.

(b) Heat energy produced, H = I² R t

In the parallel combination of resistances, current increases due to a decrease in effective resistance.
As the heat energy produced is directly proportional to the square of the current, it can be concluded that the parallel combination gives more heat energy.

Answer:

Ans 26. (a) 


(b) The process of asexual reproduction in yeast is called budding.

Answer:

(a) Parts I and III will appear blue black in colour which indicates the presence of starch in these regions.
(b) Part II will not appear blue black in colour because starch will be missing from that part. The black paper in region II will prevent the sunlight from reaching that region, as a result of which no starch synthesis would occur.