13.1 (a) Two stable isotopes of lithium ${}_3{}^6\mathit{L}\mathit{i}$ and ${}_3{}^7\mathit{L}\mathit{i}$ have respective abundances of 7.5% and 92.5%. These isotopes have masses 6.01512 u and 7.01600 u, respectively. Find the atomic mass of lithium.

(b) Boron has two stable isotopes, ${}_5{}^{10}\mathit{B}$ and ${}_5{}^{11}\mathit{B}$ . Their respective masses are 10.01294 u and 11.00931 u, and the atomic mass of boron is 10.811 u. Find the abundances of ${}_5{}^{10}\mathit{B}$ and ${}_5{}^{11}\mathit{B}$ 10.

The distance of closest approach of an alpha particle fired towards gold nucleus with kinetic energy k is r₀. The distance of closest approach when the alpha particle is fired towards same nucleus with kinetic energy 4k will be

Find the mass number of an atom whose radius is half of that of a given atom of mass number 192.

A nuclear fusion reaction is given by   If atomic mass of He is 4.0026 amu and that of O is 15.9994 amu then the Q-value of the reaction will be approximately

A radioactive simple is undergoing a decay. At any time t₁, its activity is A and another time t₂, the activity is $\frac{A}{5}.$ <!-- [if gte mso 9]><xml> </xml><![endif]--> What is the average life time for the sample?

A sample contains 10^-2kg each of two substances A and B with half lives 4s and 8s respectively. The ration of their atomic weights is 1 : 2. The ratio of the amounts of A and B after16s is $\frac{x}{100}$ . The value of x is ______.