JEE Main 2026 — Chemistry Inorganic Chemistry

In d-block elements, the stability of higher oxidation states increases down a group. Therefore, $Mo(VI)$Mo(VI) and $W(VI)$W(VI) are more stable than $Cr(VI)$Cr(VI). Statement A is incorrect.

The most stable oxidation state for lanthanoids is $+3$+3. Ions like $Ce^{4+}$Ce4+ and $Tb^{4+}$Tb4+ tend to gain an electron to achieve the $+3$+3 state, acting as oxidants. Conversely, $Eu^{2+}$Eu2+ and $Yb^{2+}$Yb2+ tend to lose an electron to achieve the $+3$+3 state, acting as reductants. Statement B is correct.

The electronic configuration of $Am$Am is $[Rn] 5f^{7} 7s^{2}$[Rn]5f77s2, which has $7$7 unpaired electrons. The electronic configuration of $Cm$Cm is $[Rn] 5f^{7} 6d^{1} 7s^{2}$[Rn]5f76d17s2, which has $8$8 unpaired electrons ($7$7 in $5f$5f and $1$1 in $6d$6d). Statement C is incorrect.

The $5f$5f electrons have a poorer shielding effect compared to $4f$4f electrons. As a result, the effective nuclear charge increases more significantly across the actinoid series, leading to a greater actinoid contraction from element to element than the lanthanoid contraction. Statement D is correct.

Thus, only statements B and D are correct.

Answer: B and D Only