COMEDK 2026 Morning Shift | d and f Block Elements Question 9 | Chemistry

B. has stable $4 \mathrm{f}^7$ electronic configuration, but acts as a strong reducing agent and converts to $\mathrm{M}^{3+}$ state. $\left(\mathrm{Eu}^{2+}, \mathrm{Ce}^{2+}, \mathrm{Pr}^{2+}, \mathrm{Dy}^{2+}\right)$

C. is a colorless ion $\left(\mathrm{Tm}^{3+}, \mathrm{Lu}^{3+}, \mathrm{Gd}^{3+}, \mathrm{Sm}^{3+}\right)$.

D. shows stable +2 oxidation state and is diamagnetic ( $\mathrm{Ce}, \mathrm{Sm}, \mathrm{Ho}, \mathrm{Yb}$ )

A: Cu B: $\mathrm{Dy}^{2+}$ C: $\mathrm{Sm}^{3+}$ D: Ho

$\mathrm{A}: \mathrm{Zn}$ B: $\mathrm{Ce}^{2+}$, C: $\mathrm{Gd}^{3+}$ D: Sm

A: Fe B: $\mathrm{Pr}^{2+}$ C: $\mathrm{Tm}^{3+}$ D: Ce

A: Ca B: $\mathrm{Eu}^{2+}$ C: $\mathrm{Lu}^{3+}$ $\mathrm{D}: \mathrm{Yb}$

COMEDK 2025 Evening Shift

MCQ (Single Correct Answer)

-0

The electronic configuration of the element with atomic number 78 is :

$[X e] 4 f^{14} 5 d^9 6 s^1$

$[K r] 4 f^{14} 5 d^8 6 s^2$

$[\mathrm{Xe}] 4 f^{14} 5 d^{10}$

$[K r] 4 f^{14} 5 d^{10}$

COMEDK 2025 Evening Shift

MCQ (Single Correct Answer)

-0

Find the correct matches.

A.	$\mathrm{Cr}_2 \mathrm{O}_7^{2-}$	P.	is predominantly a basic compound.
B.	$\mathrm{FeCr}_2 \mathrm{O}_4$	Q.	is predominantly a acidic compound
C.	$\mathrm{CrO}_3$	R.	forms yellow chromate on reaction with $\mathrm{Na}_2 \mathrm{CO}_3$ in air.
D.	$\mathrm{CrO}$	S.	is interconvertible with $\mathrm{MO}_4^{2-}$ depending on the pH of the medium.

$\mathrm{A}=\mathrm{R} \quad \mathrm{B}=\mathrm{S} \quad \mathrm{C}=\mathrm{P} \quad \mathrm{D}=\mathrm{Q}$

$\mathrm{A}=\mathrm{S} \quad \mathrm{B}=\mathrm{R} \quad \mathrm{C}=\mathrm{P} \quad \mathrm{D}=\mathrm{Q}$

$\mathrm{A}=\mathrm{R} \quad \mathrm{B}=\mathrm{Q} \quad \mathrm{C}=\mathrm{S} \quad \mathrm{D}=\mathrm{P}$

$\mathrm{A}=\mathrm{S} \quad \mathrm{B}=\mathrm{R} \quad \mathrm{C}=\mathrm{Q} \quad \mathrm{D}=\mathrm{P}$

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