Chemistry - PERIODIC TABLE Question with Solution | TestHub

Statement (A) is correct because the energy required to remove an electron from $M(g)$ to form $M^{+}(g)$ (ionization energy) is equal in magnitude to the energy released when $M^{+}(g)$ gains an electron to return to $M(g)$ (electron gain enthalpy).

Statement (B) is correct because Zn ($3d^{10}4s^2$), Cd ($4d^{10}5s^2$), and Hg ($5d^{10}6s^2$) all belong to Group 12 and contain exactly 10 electrons in their $(n-1)d$ subshell.

Statement (C) is incorrect because spin multiplicity increases with the number of unpaired electrons; thus, the correct order is $Mn=M{n}^{+2}>M{n}^{+4}>M{n}^{+6}>M{n}^{+7}$.

Statement (D) is incorrect because ionization involves only the loss of electrons, while the number of protons in the nucleus remains constant.