The stabiliy of nuclies has been explained in terms of binding energy. Higher is binding energy, more is stabliliy to nucleus. The binding energy is written as `B.E = 931.478 xx Delta m' MeV`m wehre `Delta m'` is mass decayed in amu. If `B.E.//"nucleon"` lies below the belt of stablilty, the nucleus undergoes `alpha-` emission in order to lower down the energy level of nucleus but its `n//p` ratio increases. To lower down the energy level of nucleus but is `n//p` ratio increases. To lower down level of nucleus loses `beta-` particles and if stability is not gained, `gamma-` emission is noticed. A radioactive element on losing on `alpha-` particles shows a loss in its mass number by `4` units and atomic number by 2 units whereas `beta-` emission leads to a gain in at.no by one units and mass no. remains same.
`._(90)^(228)Th overset(-alpha)(rarr) A`,If `Th` belongs to `III gp`of periodic table, then `'A'` belongs to:

Options

A. `I gp`.
B. `II gp`.
C. `III gp`.
D. Zero `gp`

Answer

`b

Explanation

`underset("IIIgp.")(._(90)^(238))Th rarr underset("II gp.")(._(88)^(234))Ra + ._(2)^(4)He`,
Elements from 89 to 103 belongs to `III gp`