The spin-only magnetic moment value of ${\mathrm{B}}_2^{+}$ species is $\times {10}^{-2}\mathrm{BM}$. (Nearest integer)
[Given $:\sqrt{3}=1.73]$

According to MOT, electronic configuration of ${\mathrm{B}}_2^{+}$ is $\mathrm{\sigma }1{\mathrm{s}}^2{\mathrm{\sigma }}^{*}1{\mathrm{s}}^2\mathrm{\sigma }2{\mathrm{s}}^2{\mathrm{\sigma }}^{*}2{\mathrm{s}}^2 {}_{\mathrm{\pi }2{\mathrm{p}}_{\mathrm{y}}}{}^{\mathrm{\pi }2{\mathrm{p}}_{\mathrm{x}}^1} \mathrm{\sigma }2{\mathrm{p}}_{\mathrm{z}}$ It has one unpaired electron. ($\mu$ ) Spin - only magnetic moment $=\sqrt{n(n+2)}$ B.M ;  n= Number of unpaired electrons

$\begin{array}{rl} & \mathrm{\mu }=\sqrt{1(1+2)}\text{B.M}\\ & \mathrm{\mu }=1.73\text{B.M}\end{array}$

Hence, correct answer is: 2