Question

If $X^{2-}$ is isoelectronic with "$O_2^{+}$" and has Z + 1 neutrons (Z is the atomic number of $X^{2-}$), then:

• A. The mass number of $X^{2-}$ is $27$
• B. The mass number of $X^{2-}$ is $57$
• C. The atomic number of $X^{2-}$ is $28$
• D. The number of protons in $X^{2-}$ is $13$

Answer 1

Answer: (A), (D)

The correct options are
A The mass number of $X^{2-}$ is $27$
D The number of protons in $X^{2-}$ is $13$

$X^{2-}$ has $16-1=15$ electrons

Thus X has $15-2=13$ electrons

$\therefore$Number of protons in $X^{2-}=13$

The mass number of $X^{2-}=13+13+1=27$