The spectral series which corresponds to the electronic transition from the levels $$n_2=5,6, \ldots$$ to the level $$n_1=4$$ is

Water is used as a coolant in a nuclear reactor because of its

Some energy levels of a molecule are shown in the figure with their wavelengths of transitions. Then :

Select the correct statements among the following :

A. Slow neutrons can cause fission in $${ }_{92}^{235} \mathrm{U}$$ than fast neutrons.

B. $$\alpha$$-rays are Helium nuclei.

C. $$\beta$$-rays are fast moving electrons or positrons.

D. $$\gamma$$-rays are electromagnetic radiations of wavelengths larger than $$\mathrm{X}$$-rays.

Choose the most appropriate answer from the options given below :