If the half-life of a radioactive material is 10 years, then the percentage of the material decayed in 30 years is

The ratio of the shortest wavelengths of Bracket and Balmer series of hydrogen atom is

If the binding energy per nucleon of deuteron $\left({ }_1 \mathrm{H}^2\right)$ is 1.15 MeV and an $\alpha$-particle has a binding energy of 7.1 MeV per nucleon, then the energy released per nucleon in the given reaction is

$$ { }_1 \mathrm{H}^2+{ }_1 \mathrm{H}^2 \rightarrow{ }_2 \mathrm{He}^4+\mathrm{Q} $$

The ratio of the time periods of the revolution of the electrons in the second and third excited states of hydrogen atom is