You are given two elements whose radii are in ratio 3:7. What will the nuclear density of the former be given by ?

2.3 x 10¹⁷ Kg m^-3

Nuclear density is constant and is 2.3 x 10¹⁷ Kg m^-3 _. Think of nuclei of all matter as a liquid drop of constant density of the given value.

Also, option 1 and 3 have order 10^-12 and that of nucleus is 10^-17. Option 4 has the wrong units. So this leaves us with option 2 alone.