Board Paper of Class 10 2009 Science (SET 3) - Solutions

What would be the colour of litmus in a solution of sodium carbonate?

Name a reducing agent that may be used to obtain manganese from manganese dioxide.

Balance the following chemical equation:

Pb(NO₃)₂(s) PbO(s) + NO₂(g) + O₂ (g)

Take down this figure into your answer book and complete the path of the ray.

Why does sky look blue on a clear day?

Why does a ray of light bend when it travels from one medium into another?

Define a combination reaction. Give one example of a combination reaction which is also exothermic.

A compound which is prepared from gypsum has the property of hardening when mixed with a proper quantity of water. Identify the compound. Write the chemical equation for its preparation. For what purpose is it used in hospitals?

What is the minimum number of rays required for locating the image formed by a concave mirror for an object? Draw a ray diagram to show the formation of a virtual image by a concave mirror.

Calculate the area of cross section of a wire if its length is 1.0 m, its resistance is 23 Ω and the resistivity of the material of the wire is 1.84 × 10⁻⁶Ω m.

An ore on heating in air produces sulphur dioxide. Which process would you suggest for its concentration? Describe briefly any two steps involved in the conversion of this concentrated ore into related metal.

Give reasons for the following observations:

(a) The element carbon forms a very large number of compounds.

(b) Air holes of a gas burner have to be adjusted when the heated vessels get blackened by the flame.

(c) Use of synthetic detergents causes pollution of water.

What is hypermetropia? State the two causes of hypermetropia. With the help of ray diagrams, show:

(i) the eye-defect hypermetropia (ii) correction of hypermetropia by using a lens

Two resistors, with resistances 5 Ω and 15 Ω are to be connected to a battery of emf 9 V so as to obtain:

(i) minimum current

(ii) maximum current

(a) Show with the help of a diagram how you would connect the resistances in each case.

(b) Calculate the strength of the total current in the circuit in each of the two cases.

(a) Which two criteria did Mendeleev use to classify the elements in his periodic table?

(b) State Mendeleev’s periodic law.

(c) Why could no fixed position be given to hydrogen in Mendeleev’s periodic table?

(d) How and why does the atomic size vary as you go:

(i) from left to right along a period?

(ii) down a group?

OR

(a) Why did Mendeleev have gaps in his periodic table?

(b) State any three limitations of Mendeleev’s classification.

(c) How does electronic configurations of atoms change in a period with increase in atomic number?

(a) What is a solenoid? Draw a sketch of the pattern of field lines of the magnetic field through and around a current carrying solenoid.

(b) Consider a circular loop of a wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right hand rule to find out the direction of the magnetic field inside and outside the loop.