1.

When radioactive substance emits an `alpha-`particle, then its position in the periodic table is lowered by.A. three placesB. one placeC. five placesD. two places

Answer» Correct Answer - D
(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.


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