Choose the correct statement from the following with reference to the d- and f - block elements:
A. Complex compounds having a transition metal in low oxidation states are formed when ligands exhibit π-acceptor and σ-bonding characters.
B. The melting point of Tc is lower than the Mo but higher than the Ru.
C. Vanadium pentachloride (VCl5) on hydrolysis gives vanadium oxytrichloride (VOCl3).
D. Alkalies have no action on actinoids.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A, C and D only
This question tests four separate facts about the d- and f-block elements. Judge each statement on its own.
A. Complex compounds having a transition metal in low oxidation states are formed when ligands exhibit π-acceptor and σ-bonding characters. — Correct. Ligands such as CO donate a lone pair to the metal (σ bond) and also accept electron density from filled metal d orbitals into their empty π* orbitals (π back bonding). This removes excess electron density from the metal and stabilises very low oxidation states, as in \( \ce{Ni(CO)4} \) and \( \ce{Fe(CO)5} \), where the metal is in the zero state.
B. The melting point of Tc is lower than the Mo but higher than the Ru. — Incorrect. The melting points are Mo 2896 K, Tc 2430 K and Ru 2607 K. Tc is lower than Mo, but it is also lower than Ru. Technetium is an irregular dip in the trend of the 4d series.
C. Vanadium pentachloride (VCl5) on hydrolysis gives vanadium oxytrichloride (VOCl3). — Correct. In the +5 state vanadium prefers to bond with oxygen rather than hold five chlorine atoms. Partial hydrolysis replaces two chlorine atoms by one oxygen atom, giving the oxohalide:
\( \displaystyle \ce{VCl5 + H2O -> VOCl3 + 2HCl} \)
D. Alkalies have no action on actinoids. — Correct. The actinoids are highly reactive metals. They are attacked by hydrochloric acid and combine with most non-metals, but alkalies have no action on them.