Density of all the nuclei is same.
Radius of nucleus is directly proportional to the cube root of mass number.

Options

A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true but R is NOT the correct explanation of A
C. A is true but R is false
D. A is false and R is true

Answer

A

Explanation

Radius of nucleus `=R=R_(0)A^(1//3)`.
So, Volume of nucleus, `V=(4)/(3)piR_(0)^(3)A`
Considering mass of proton = mass of neutron = m
The mass of the nucleus = M =mA
So, density `="M/V"=(mA)/((4)/(3)piR_(0)^(3)A)=(m)/((4)/(3)piR_(0)^(3))`
So, the mean density is independent of mass number.
So, assertion and reason both are true and the reason properly explains the assertion.