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Q.
Mass defect of an atom refers to
Nuclei
Solution:
$Mc ^{2}+( B \cdot E )=\left( N _{ mN }+ Z _{ mP }\right) c ^{2}$
where,
$M _{ c }=$ total mass of nucleus.
$N _{ m N }=$ total mass of neutrons
$N _{ mP }=$ total mass of protons