Question

Atomic number and mass number of an element $M$ are $25$ and $52$ respectively. The number of electrons, protons and neutrons in $M ^{2+}$ ion are respectively

• A. 25,25 and 27
• B. 25,27 and 25
• C. 27,25 and 27
• D. 23,25 and 27

Answer 1

Answer: (D)

Atomic number $=25$
Mass number $=52$
Number of proton $=$ Atomic number $=25$
Number of neutron $=($ Mass number $-$ Atomic number)
$52-25=27$
Number of $e ^{-}=$Number of protons,
but $M ^{2+}$ ion means $2 e ^{-}$ are removed
$\therefore $ Number of $e ^{-}=$Number of protons $-2$
$=25-2=23$