Question

Assertion: Calcium floats over water during reaction with water.
Reason: Calcium reacts with water less vigorously so that heat evolved is not sufficient for the hydrogen formed, to catch fire. The bubbles of hydrogen gas formed stick to the surface of the water calcium.
(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) Both assertion and reason are incorrect.

Answer 1

In the above question, assertion about floating of calcium is given and reason is also given where reaction between calcium and water is discussed. We have to analyse both the points to choose the best suitable alternative. We know reactivity of Group 2 elements with water is comparatively less than that of Group 1 and not much heat is evolved.

Complete answer:
The chemical element Calcium has atomic number 20. It is the fifth element and the third most abundant metal in the earth’s crust. Calcium ions dissolved in water form deposits in pipes and boilers. When water contains too much calcium or magnesium, it is called hard water. In contact with air, calcium develops an oxide and nitride coating, which protects it from further corrosion.
Calcium metal is an alkaline earth metal found in Group 2 and reacts with water to form calcium hydroxide and hydrogen gas. Group 2 metals don’t have as high solubility in water as Group 1, which is why the reaction of calcium in water goes faster in warm water. The reaction is not as vigorous or dangerous as the highly reactive alkali metals Na, K, or Li found in Group 1.
As we know that calcium reacts slowly with water. The reaction of calcium and hydrogen leads to formation of calcium hydroxide and hydrogen which is illustrated below:
${\text{Ca + 2}}{{\text{H}}_{\text{2}}}{\text{O }} \to {\text{ Ca(OH}}{{\text{)}}_{\text{2}}}{\text{ + }}{{\text{H}}_{\text{2}}}$
So, the heat released during this process is not sufficient for the hydrogen to catch fire, hence, the bubbles of hydrogen gas stick to the surface of the metal and hence, starts floating on water.
Since, both assertion and reason are correct and reason is the correct explanation for assertion.
So, option A is the correct option.

Note:
Calcium compounds are more or less water soluble. During the reaction of calcium and water, at first, the calcium sinks in the water and then , after an hour, bubbles of hydrogen evolve which stick to the surface of the metal and hence, it floats on water.