Assertion : The position of an element in periodic table after emission of one ( ) and two ( )-particles remains unchanged. Reason : Emission of one ( ) and two ( )-particles give isotope of the element which acquires same position in periodic table.

Step-by-step solution

The loss of one ( )-particle will reduce the mass number by four and atomic number by two. Subsequent two ( )-emissions will increase the atomic number by two without affecting the mass number. Hence, the new element will be only an isotope of the parent nucleide and hence its position in the periodic table remains unchanged.