When radioactive substance emits an `alpha-`particle, then its position in the periodic table is lowered by.

Options

A. three places
B. one place
C. five places
D. two places

Answer

D

Explanation

(d) When an `alpha-`particle is emitted from the nucleus of a radioactive atom, the atomic number is reduced by `2` and mass number is reduced by `4`.
`._Z X^A rarr ._(Z-2)Y^(A - 4) + ._2He^4 (alpha-`particle)
Elements are placed in the periodic table according to their atomic number. The emission of an `alpha-`particle from the atom of an element reduces its atomic number by `2`, so the element is converted into a new element which occurs `2` steps earlier in the periodic table.