Assertion: In taking into account the fact that any object which floats must have an average density less than that of water, during World War I, a number of cargo vessels were made of concrete.
Reason: Concrete cargo vessels were filled with air.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. if assertion is true but reason is false.
D. if both assertion and reason are false.

Answer

B

Explanation

The density of concrete of course, is more than that of water and block of concrete will sink like a stone, if dropped into water. Concrete cargo were filled with air and as such, average density of cargo vessels.
`=(mass of concrete+mass of air )/(volume of concrete+volume of air)`
it follows that the average density of cargo vessels must be less than that of water. As a result the concrete cargo vessels did not sink.