Lakhmir Singh Manjit Kaur Chemistry 2020 2021 for Class 10 Science Chapter 8 - Model Test Paper 2

Answer:

Solutions having higher hydrogen ion concentration will be more acidic. So, the solution "A"  is more acidic as it has a lower pH.

Answer:

 (i) Positive geotropism - roots
(ii) Negative geotropism - shoots

Answer:

Eye colour or hair colour of a human being is an example of inherited character whereas body weight is an example of acquired character.

The basic difference between inherited and acquired characters is that inherited characters are passed on from parent to offspring. On the other hand, acquired characters are acquired by an individual during his/her lifetime depending upon his/her lifestyle.

Answer:

Redox reactions are those reactions in which simultaneous oxidation and reduction of chemical species are involved. In a redox reaction, one specie is reduced and another is oxidized.

Magnesium and oxygen combine to form magnesium oxide,
$2\mathrm{Mg}+{\mathrm{O}}_2\to 2\mathrm{MgO}$

Since magnesium gains oxygen, we can say that it gets oxidized.

Answer:

A solar cell panel is a device to convert light energy from the sun into electrical energy. Two advantages of solar cell panels are as follows:

(i) Solar cell panels are eco-friendly. They use the sun's light energy, which is unlimited and a natural source.

(ii) They are very easy to operate compared to other power sources of renewable type.

Answer:

Following chemical reaction an example of displacement reaction and redox reaction.

Fe₂O₃ + 2Al → Al₂O₃ + 2Fe

As aluminium is more reactive than iron it will displace iron from iron oxide and forms aluminium oxide. 
Iron loses oxygen and aluminium gains oxygen, so iron is reduced and aluminum is oxidized.

Since it is a highly exothermic reaction, it is used for welding purposes.
 

Answer:

A chemical equation is a symbolic representation of the process that occurs in a chemical reaction. A chemical equation is written with the reactants on the left side of an arrow and the products of the chemical reaction on the right side of the equation.
The law of conservation of mass states that mass can neither be created nor be destroyed. Hence, in a chemical reaction, the total mass of the reactants should be equal to the total mass of the products.
Balanced chemical equation: ${\mathrm{BaCl}}_2\left(\mathrm{aq}\right)+{\mathrm{Na}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to 2\mathrm{NaCl}\left(\mathrm{aq}\right)+{\mathrm{BaSO}}_4\left(\mathrm{s}\right)$

Answer:

(a) The atomic number of an element will be 20.

(b) Electronic configuration of the element is 2, 8, 8, 2. So, from this, we can conclude that it belongs to the second group of the periodic table. In modern periodic table elements with similar properties are placed in the same group. Out of the given options magnesium belongs to the same group as the electronic configuration of magnesium is 2, 8, 2.

Answer:

(a) The general formula for alkenes is C_nH_2n. 
Out of given options C₂H_4, C₃H₆ are alkenes.

(b) Addition reactions are generally shown by unsaturated molecules i.e. molecules having a double or triple bond. 
So, out of given options C₃H₆, C₂H₂ will give an addition reaction.

 

Answer:

(a) When the live wire comes in contact with the neutral wire, the electric supply is said to be short-circuited. Due to short-circuiting in electric supply, a high amount of current flows in the circuit, which may damage various electric appliances or even start a fire.

(b) The function of the earth wire in the electrical instruments is to provide an immediate path to excess or unnecessary current in the circuit into the ground. It reduces the chances of getting a shock.

(c) (i) The usual current rating of the fuse wire in the line which runs lights and fans is 5 A.
(ii)The usual current rating of the fuse wire in the line which runs appliances of 2kW or more power is 15 A.

Answer:

(a) A convex lens that is used to produce a magnified image of an object in a magnifying glass (called a hand lens in laboratory contexts).

(b) A concave lens (minus powered) is used to correct the defect of a myopic eye. 

(c) A convex lens forms a real image of the same size and inverted in nature when the object is placed at point '2f' of the convex lens. 

The focal length of the given lens = 10.5 cm

Hence, the object should be placed 21 cm away from the pole to form the required image.

 

Answer:

A spectrum is a band of colors. It is produced when component colors of light are separated at different degrees by refraction through a prism. A spectrum of light is shown in the diagram given below:


There are mainly seven colors present in the spectrum of light. i.e. Violet, Indigo, Blue, Green, Yellow, Orange, and Red.

Answer:

(a) An embryo gets nourishment inside the mother's body through placenta. It is a special disc-like organ that develops in the fourth week of pregnancy. It establishes an intimate connection between the foetal membrane and the uterine wall via umbilical cord.

Function of Placenta:

• The exchange of materials between the blood of mother and foetus takes place through placenta.
• It provides nutrition to the foetus.
• It also serves as the respiratory (by allowing exchange of oxygen and carbon dioxide) and excretory organ (by allowing excretion of waste material of foetus into mother's blood) of the foetus.

Answer:

The formation of a new species by evolution or any genetic modification of the previously existing species in a population is called speciation.

Following are the factors responsible for speciation:
1. Genetic drift - The accidental change in the frequency of genes in a small population is called genetic drift.
2. Natural selection - It is a process that results in an increased survival and reproductive success of individuals that are well adjusted to the environment.
3. Reproductive isolation - It refers to the absence of other reproductively compatible plants in the same area.
4. Geographical isolation - It refers to a type of barrier which prevents the mating between members of a species due to geographical barriers.

Answer:

(a) (i) Seminal vesicles - The secretions of seminal vesicles contain many proteins and enzymes and thus provide nutrition to the developing sperms.

(ii) Prostate gland - The prostate gland secretes a slightly alkaline fluid that lubricates the sperms and neutralises the acidity of the vaginal tract.

(b) Two important functions of testes are -

(i) Production of sperms

(ii) Production of a hormone called testosterone, which brings about secondary sexual characters in boys

Answer:

(a) Electronic configuration of sodium = 2, 8, 1
Electronic configuration of chlorine = 2, 8, 7

(b)


(c) 

Sodium will lose one electron and become electron deficient while chlorine gains one electron and becomes electron rich.

(d) Properties of ionic compound:
(i) They are hard because of the strong force of attraction between positive and negative ions.
(ii) They have high melting and boiling point.
(iii) They are generally soluble in water but insoluble in inorganic solvents.

 

Answer:

(a) Metals in the bottom of the reactivity series are found in the free state. For eg. gold, platinum, silver, etc.

(b) Metal can be extracted from its oxide ore by electrolytic reduction. Aluminium metal can be extracted by electrolytic reduction of molten aluminium oxide.

$2{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{l}\right)\to 4\mathrm{Al}\left(\mathrm{l}\right)+3{\mathrm{O}}_2\left(\mathrm{g}\right)$

(c) Zinc is extracted from its carbonate ore by calcination process in which carbonate ore is heated strongly in the absence of air to convert it into zinc oxide.

$\underset{\mathrm{zinc} \mathrm{carbonate} \mathrm{ore}}{{\mathrm{ZnCO}}_3\left(\mathrm{s}\right)}\stackrel{\mathrm{calcination}}{\to }\mathrm{ZnO}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$

Zinc sulphide is extracted from its sulphide ore by roasting process in which sulphide ore is heated strongly in the presence of air to convert it into zinc oxide.

$\underset{\mathrm{zinc} \mathrm{sulphide}}{2\mathrm{ZnS}\left(\mathrm{s}\right)}+3{\mathrm{O}}_2\left(\mathrm{g}\right)\stackrel{\mathrm{roasting}}{\to }2\mathrm{ZnO}\left(\mathrm{s}\right)+2{\mathrm{SO}}_2\left(\mathrm{g}\right)$
 

Answer:

(a) An electric motor works on the magnetic effect of current. 

(b) An electric generator works on the phenomenon of electromagnetic induction.

(c) An electric motor converts electrical energy into mechanical energy.

(d) The electric motor works on the principle of Fleming's left-hand rule. It states that when an electric current is passed through a conductor placed in a magnetic field, it experiences a force in a direction perpendicular to the direction of both the electric field and magnetic field. That force moves the coil of the electric motor, and that's how electric energy is converted into mechanical energy in an electric motor. 

(e) An electric generator works on the principle based on Fleming's right-hand rule. Which states that when a coil of insulated copper wire is forced to rotate inside a magnetic field, then electric current is induced. That's how an electric generator converts mechanical energy into electrical energy. 

Answer:

(a) When an object is placed beyond '2f' of a convex lens, the image formed is diminished and real in nature.

(b) Power of a lens is indirectly proportional to its focal length. i.e. $P\propto \frac{1}{f(\mathrm{in} \mathrm{meter})}$

According to the above relation, the lens with a smaller focal length would have greater power. So, lens A has greater power.

(c)



Characteristics of the image formed above:

(i) Image is virtual
(ii) Image is erect
(iii) Image is enlarged


 

Answer:

(a) Rabbit and deer belong to the same trophic level. Both are herbivores and occupy the second trophic level.

(b) First trophic level is occupied by plants whereas third trophic level is occupied by carnivores or secondary consumers.
Plants are autotrophic in nature i.e. they can produce their own food and thus are also called producers. Example: plants
Whereas organisms which occupy the secondary trophic levels are called consumers. These organisms are meat eaters and depend on other organisms for their food needs. Example: tiger

Answer:

Ozone layer is a layer consisting of ozone molecules which acts as a protective layer for life on the earth. 

It protects the earth by absorbing harmful ultraviolet radiations of the sun. These radiations, if reach the earth’s surface, can cause skin cancer.

Then, this free oxygen atom combines with an oxygen molecule to form ozone.

CFC stands for chlorofloro carbon. 
The ozone layer is getting depleted by the action of chlorofluorocarbons (CFCs) used as coolant in refrigerators and perfumes. The CFCs are acted upon by UV rays in the stratosphere, liberating the Cl atoms, which act as catalysts to degrade ozone into molecular oxygen.

Answer:

When an object is placed at the radius of curvature of a concave mirror, the image formed has the same size as that of the object.

Hence, in given the case, the size of the image would be the same as the size of the object.
 

Answer:

(a)


(b) (i) The function of the first prism is to split the white light into seven colors.
(ii) The function of the second prism is to recombine them back into white light.

Answer:

(a) Out of given solutions, "B" will be weakly alkaline. On the pH scale, the higher the value of pH stronger will be the base.

(b) Out of given solutions, "E" will be strongly alkaline. On the pH scale, the higher the value of pH stronger will be the base.

(c) Out of given solutions, "A" will be weakly acidic. On the pH scale, lower the value of pH stronger will be the acid.

(d) Out of given solutions, "C" will be strongly acidic. On the pH scale, lower the value of pH stronger will be the acid.

Answer:

(a) Decomposition of water is a very slow process and addition of dilute sulphuric acid increases the rate of decomposition of water.

$2{\mathrm{H}}_2\mathrm{O}\stackrel{{\mathrm{H}}^{+}}{\to }2{\mathrm{H}}_2+{\mathrm{O}}_2$

(b) Gas X is hydrogen, which will accumulate at the cathode, as positively charged hydrogen ions will move towards the negatively charged cathode electrode.

(c) Gas Y is oxygen, which will accumulate at the anode, as negatively charged oxygen ions will move towards the positively charged anode electrode.

(d) When electricity is passed in water, it splits water into two hydrogen ions and one oxygen ions.

Answer:

(a) (i) response of plant to sunlight - phototropism
     (ii) bending of stem of plant towards sunlight -  phototropism
     (iii) bending of root of plant away from sunlight - geotropism

(b) Auxin is the plant hormone which makes the plant respond to sunlight.

Answer:

(a) The chemical whose accumulation in leg muscles produce cramps is called lactic acid.
(b) Lactic acid is a product of anaerobic respiration.
(c) The person can get relief by placing his legs in warm water for some time. This improves the circulation of blood and removes the accumulation of lactic acid.