Class 10 Science - Chapter Chemical reaction and Equation NCERT Solutions | A shiny brown coloured element ‘X&

Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.

Give an example of a double displacement reaction other than the one given in activity 1.10.

Why is respiration considered an exothermic reaction? Explain.

Identify the substances that are oxidised and the substance that are reduced in the following reactions.

    (i)    4Na(s)   +   O₂(g)    →    2Na₂O(s)
    (ii)   CuO(s)   +   H₂(g)    →    Cu(s)   +   H₂O(l)

Translate the following statements into chemical equations and then balance them.

(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and sulpur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Explain the following terms with one example each.

(a) Corrosion
(b) Rancidity

Explain the following in terms of gain or loss of oxygen with two examples each.

(a) Oxidation
(b) Reduction

Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.

Write the balanced chemical equation for the following and identify the type of reaction in each case.

(a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g

What is a balanced chemical equation? Why should chemical equations be balanced?

Did Döbereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.

What is a good source of energy?

Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?

What are trophic levels? Give an example of a food chain and state the different trophic levels in it.

What changes can you make in your habits to become more environment-friendly?

What is the difference between a reflex action and walking?

What is the importance of DNA copying in reproduction?

If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?

Define the principal focus of a concave mirror.

You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?

What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?

Name two metals which are found in nature in the free state.

Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.

What is the function of digestive enzymes?

Give an example of a plant hormone that promotes growth.

Choose the correct option.

A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each

       (a) two revolutions         (b) one revolution
       (c) half revolution           (d) one-fourth revolution

If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?

How are the alveoli designed to maximise the exchange of gases?

Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?

In the Modern Periodic Table, which are the metals among the first ten elements?