Akademik Lomonosov, sometimes seen in the news, is a/an _____________.

 Read the following statements about the use of coal and petroleum as energy sources.

(i) These are energy sources formed from biomass.

(ii) Inexhaustible energy sources when used continuously.

(iii) On combustion release oxides of sulphur and nitrogen.

(iv) Clean and eco-friendly sources of energy.

Correct statements are:

Elaborate the full form of CNG.

PASSAGE
Nuclear fission is the phenomenon of splitting of an unstable nucleus of a heavy atom into two medium-weight nuclei due to bombardment with slow-moving neutrons, with the release of enormous amount of energy.

Nuclear fusion is the phenomenon of combining or fusing two or more lighter nuclei to form a stable heavier nucleus with the liberation of enormous amount of energy.

Now consider four materials -$\mathrm{W}, \mathrm{X}, \mathrm{Y}$ and $\mathrm{Z}$ with mass numbers $2, 35, 135$ and $239$ respectively.
With regard to the above, answer the following question:

The disposal of wastes in a nuclear power plant is a big problem because they are: