An $\alpha$-particle of energy $E$ is liberated during the decay of a nucleus of mass number 236. The total energy released in this process is

The related effort to derive the properties of a bigger, more complex system from the properties and interactions of its constituent simpler parts is

The ratio of the wavelengths of radiation emitted when an electron in the hydrogen atom jumps from 4th orbit to 2 nd orbit and from 3rd orbit to 2 nd orbit is

The half lives of two radioactive material $A$ and $B$ are respectively $T$ and $2 T$. If the ratio of the initial masses of the materials $A$ and $B$ is $8: 1$. Then, the time after which the ratio of the masses of the materials $A$ and $B$ becomes $4: 1$ is