English Medium Class 10 - CBSE Important Questions for Science

The colour of the solution observed after 30 minutes of placing zinc metal in copper sulphate solution is ______.

Dil. HCl is added to Zn granules. How will you prove that chemical change has taken place here? Support your response with two arguments.

A chemical reaction in which exchange of ions occurs between the reactants is known as ______.

When lead nitrate is heated strongly in a boiling tube, two gases are liberated and a solid residue is left behind in the test tube.

1. Name the type of chemical reaction and define it.
2. Write the name and formula of the coloured gas liberated.
3. Write the balanced chemical equation for the reaction.
4. Name the residue left in the test tube and state the method of testing its nature (acidic/basic).

Write balanced chemical equation for the following word equation.

Lead nitrate + Potassium iodide → Lead iodide + Potassium nitrate

Is this a double displacement reaction? Justify your answer. Name the compound precipitated and write the ions present in it.

Write the method of preparation of Ca(OH)₂. What happens when CO₂ is passed through it? Write balanced chemical equation for the reaction involved.

You are asked to prepare hard water in your laboratory. Select a group from the following groups of salts, any salt of which you may dissolve in distilled water to obtain hard water.
(A) NaCl; Na2SO4; KCl
(B) NaCl; CaCl2; KCl
(C) CaCl2; CaSO4; MgSO4
(D) Na2SO4; CaSO4; MgSO4

Out of HCl and CH₃COOH, which one is a weak acid and why? Describe an activity to support your answer.

Out of three metals P, Q and R, P is less reactive than Q and R is more reactive than P and Q both. Suggest an activity to arragne P, Q and R in order of their decreasing reactivity. 

Answer the following question.
Identify the acid and the base from which sodium chloride is obtained. Which type of salt is it? When is it called rock salt? How is rock salt formed?

A compound which is prepared from gypsum has the property of hardening when mixed with water. identify the compound and write its formula. How is this compound prepared? Describe it in the form of a chemical equation only.

One of the events that does not occur during photosynthesis is ______.

A small amount of copper oxide was taken in a beaker and dilute hydrochloric acid was added with continuous stirring of the solution. Name the compound formed and state the colour of its solution. Write the balanced chemical equation for the reaction that occurs. Based on the reaction, state the nature (acidic/basic) of copper oxide.

An aqueous solution of a salt turns blue litmus to red. The salt could be the one obtained by the reaction of ______.

What is atmospheric refraction? Use this phenomenon to explain the following natural events:

Advanced sun-rise and delayed sun-set.

Draw diagrams to illustrate your answers.

In the following ray diagram the correctly marked angle are:

(a) ∠i and ∠e

(b)  ∠A and ∠D

(c) ∠i, ∠e and ∠D

(d) ∠r, ∠A and ∠D

A person needs a lens of power -5.5 dioptres for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (i) distant vision and (ii) near vision?

The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?

What happens to the image distance in the eye when we increase the distance of an object from the eye?

Explain why the planets do not twinkle.