The mass of a neutron is approximately the same as that of:

Assertion: Isobars are the elements having same mass number but different atomic number.
Reason: Neutrons and protons are present inside the nucleus.

Which of the following is true for a sample of $U^{235}$ and $U^{238}$ isotopes?

Highly energetic electrons are bombarded on a target of an element containing $30$ neutrons. The ratio of the radius of the nucleus to that of a Helium nucleus is $14^{1/3}$. The atomic number of the nucleus will be

Calculate the height of the potential barrier for a head-on collision of two deuterons. (Radius of deuteron is $2$ fm).

What is the approximate percentage of the total mass of an atom that is concentrated in its nucleus (in $\%$)?