1
COMEDK 2025 Evening Shift
MCQ (Single Correct Answer)
+1
-0

Choose the correct metal/ ion from the brackets which -------------------------

A. has chemical reactivity similar to that of the first few members of the Lanthanoids $(\mathrm{Zn}, \mathrm{Ca}, \mathrm{Fe}, \mathrm{Cu})$.

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
A: Cu B: $\mathrm{Dy}^{2+}$ C: $\mathrm{Sm}^{3+}$ D: Ho
B
$\mathrm{A}: \mathrm{Zn}$ B: $\mathrm{Ce}^{2+}$, C: $\mathrm{Gd}^{3+}$ D: Sm
C
A: Fe B: $\mathrm{Pr}^{2+}$ C: $\mathrm{Tm}^{3+}$ D: Ce
D
A: Ca B: $\mathrm{Eu}^{2+}$ C: $\mathrm{Lu}^{3+}$ $\mathrm{D}: \mathrm{Yb}$
2
COMEDK 2025 Evening Shift
MCQ (Single Correct Answer)
+1
-0
Which of the following alkene on reductive ozonolysis gives ketones only as the product
A
1, 2-butadiene
B
1, 4-cyclohexadiene
C
But-2-ene
D
2,3-dimethylbut-2-ene
3
COMEDK 2025 Evening Shift
MCQ (Single Correct Answer)
+1
-0
The oxidation number of potassium in $\mathrm{K}_2 \mathrm{O}, \mathrm{K}_2 \mathrm{O}_2$ and $\mathrm{KO}_2$ respectively are:
A
$+1,+2,+4$
B
$+1,+2,+1$
C
$+1,+1,+1$
D
$+2,+1,+1$
4
COMEDK 2025 Evening Shift
MCQ (Single Correct Answer)
+1
-0
For a cell $2 \mathrm{M}_{(\mathrm{S})}+\mathrm{O}_2(\mathrm{~g})+4 \mathrm{H}^{+} \rightarrow 2 \mathrm{M}^{2+}(\mathrm{aq})+2 \mathrm{H}_2 \mathrm{O}_{(\mathrm{l})}$ the $\mathrm{E}^0$ cell $=+1.67 \mathrm{~V}$. When $\left[\mathrm{M}^{2+}\right]$ is $1.0 \times 10^{-3} \mathrm{M}$ and $\mathrm{p}\left(\mathrm{O}_2\right)$ is 0.1 atm , the EMF of the cell becomes +1.57 V . Calculate the pH of the electrochemical cell.
A
3.49
B
2.95
C
5.24
D
12.01
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