A positron is emitted from ${ }^{23} \mathrm{Na}_{11}$. The ratio of the atomic mass and atomic number of the resulting nuclide is

$\pi $ mesons can be

The atoms of same element having different masses but same chemical properties, are called

Of the following pairs of species which one will have the same electronic configuration for both members?

The mass number of nucleus having radius equal to half of the radius of nucleus with mass number $192$ is:

Assertion $(A):$ Forces acting between proton-protn $\left(f_{p p}\right)$, proton-neutron $\left(f_{p p}\right)$ and neutron-neutron $\left(f_{n n}\right)$ are such that $f_{p p} < f_{p n}=f_{n n}$

Reason $(R):$ Electrostatic force of repulsion between two protons reduces net nuclear forces between them.