Question

The species which has its fifth ionisation potential equal to $340$ eV is:

• A. $B^{+}$
• B. $C^{+}$
• C. B
• D. C

Answer 1

Answer: (C)

B

$E=340eV$

$E=13.6\frac{z^2}{n^2}$

for, $n=1$

$340=13.6\frac{z^2}{1^2}$

$z^2=\frac{3400}{13.6}$

$z=\sqrt{25}=5$

Element with atomic number $5$ is Boron.