Which physical quantity is measured in barn?

An atom of mass number $15$ and atomic number $7$ captures an $\alpha$-particle and then emits a proton. The mass number and atomic number of the resulting product will respectively be

Which is the correct unit for measuring nuclear radii?

Match the following fundamental forces of nature with their relative strength:

List-$I$	List-$II$
$(A)$ Strong nuclear force	$(i)$ $10^{-2}$
$(B)$ Weak nuclear force	(ii) $1$
$(C)$ Electromagnetic force	(iii) $10^{-39}$
$(D)$ Gravitational force	(iv) $10^{-13}$

The ratio of the nuclear radii of elements with mass numbers $216$ and $125$ is

Which of the following pairs of nuclei represents isotones?