Question

Assertion : Sodium reacts with water, producing a hissing sound.
Reason : Sodium reacts with water and produces hydrogen gas.
(A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
(B) Both Assertion and Reason are correct, but Reason is not the correct explanation for Assertion.
(C) Assertion is correct, but Reason is incorrect.
(D) Assertion is incorrect, but the Reason is correct.

Answer 1

Hint: This question can be solved by understanding the reaction of sodium with water. Reaction of sodium with water is exothermic. Exothermic reaction means that the reaction releases heat, that is the reaction releases energy. It forms NaOH as a by-product.

Complete Step by step solution
The reaction of sodium with water is as follows,
 $ 2Na + 2{H_2}O \to 2NaOH + {H_2} \uparrow $
The reactants in this reaction are metallic sodium and water. The product obtained in this reaction is hydrogen gas and sodium hydroxide. Oxidation reaction is loss of electrons and reduction reaction is gain of electrons. Oxidation reaction proceeds with increase in oxidation number and reduction reaction proceeds with decrease in oxidation number. In this reaction the oxidation state of sodium changes from \[0{\text{ to }} + 1\], hence it undergoes oxidation. Oxidation state of hydrogen changes from \[ + 1{\text{ to }}0\], hence it undergoes reduction. This reaction is so energetically favourable and it produces a lot of heat, so it is exothermic.
The hydrogen gas released produces a hissing sound. Hence, both assertion and reason are correct and reason is the correct explanation for assertion.
The correct answer is option A.

Note
Hydrogen is a chemical element used in the upgrading of fossil fuels. Various reactions in industries are known as hydrogenation reactions in which hydrogen gas is added to the subset. In power stations hydrogen gas is used as a coolant. Hydrogen is used as shielding gas in welding methods and rotor coolant in electrical generators.