The spin only magnetic moment of a metal ion in aqueous solution (atomic number 29) is about 2BM. The valency of metal is ___.

Given atomic number $\mathrm{Z} = 29\left(\mathrm{Cu}\right)$[Ar]4s¹3d¹⁰

Number of unpaired electrons = 1
So, magnetic moment = $\sqrt{\left(\mathrm{n}\right(\mathrm{n}+2) )} =\sqrt{\left(1\right(1+2) )} =\sqrt{(3 )} = 1.73 \mathrm{BM}$
Hence, the valency of metal is 2.