(A): Mass and energy are not conserved separately, but are conserved as a single entity called mass - energy.
(R) : Mass and energy conservation can be obtained by Einstein equation for energy.

• The concept of "mass-energy equivalence" states that mass and energy are conserved as a single thing rather than separately.
•  Using Einstein's famous formula $\mathrm{E}={\mathrm{mc}}^2$, a physical system's energy E is calculated as the square root of its mass m and light speed c. 
• Because one may select units in which c=1, and therefore E = m, this conclusion is commonly referred to as "the equivalence of mass and energy" or simply "mass-energy equivalence."

Hence the correct answer is Both ‘A’ and ‘R’ are true and ‘R’ is the correct explanation of ‘A’.