Question

Sodium in water catches fire due to formation of,
(a) hydrogen gas and evolution of heat
(b) nitrogen gas and evolution of heat
(c) hydrogen gas and absorption of heat
(d) sulphur gas

Answer 1

Hint: Sodium atom when is made to react with the water, forms sodium ions and hydroxyl
- ions along with the liberation of the gas and this reaction is exothermic in nature i.e. there is
evolution of heat. Now solve it.

Complete Solution :
First let's discuss sodium. Sodium is alkali metal which belongs to the s-block element and has the atomic number as 11 and the mass number as 23. It is very soft and so soft that it could be easily cut with a knife and in its outermost shell it has one electron and has a strong tendency to lose the electron to acquire the stable electronic configuration of the nearest noble gas i.e. the neon.

- Now considering the statement:
When sodium is made to undergo reaction with the water, it results in the formation of ions i.e. the sodium ions and the hydroxyl ions along with the formation of the hydrogen gas and a lot of heat is also released. The reaction occurs as:
$2Na+2{{H}_{2}}O\to 2N{{a}^{+}}+2O{{H}^{-}}+{{H}_{2}}\uparrow +\text{ }heat$

- Due to the formation of a large amount of heat, the hydrogen gas so released, catches fire immediately.
So, thus Sodium in water catches fire due to formation of hydrogen gas and evolution of heat.
So, the correct answer is “Option A”.

Note: The reaction of sodium with the water is known as the exothermic reaction. Exothermic reactions are those reactions in which heat is released when the reaction takes place and in the above reaction, heat is evolved, so is an exothermic reaction.