MCQ
Among Group $16$ elements, which one does $NOT$ show $-2$ oxidation state?
- A$\mathrm{Se}$
- B$\mathrm{Te}$
- ✓$\mathrm{Po}$
- D$0$
Selenium shows $-2,+2,+4$ and $+6$ oxidation states
Tellurium shows $-2,+2,+4$ and $+6$ oxidation states
Polonium shows $+2$ and $+4$ oxidation states
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| $Pb ^{2+} / Pb$ | $-0.13 V$ |
| $Ni ^{2+} / Ni$ | $-0.24 V$ |
| $Cd ^{2+} / Cd$ | $-0.40 V$ |
| $Fe ^{2+} / Fe$ | $V-0.44 V$ |
To a solution containing $0.001 M$ of $X ^{2+}$ and $0.1 M$ of $Y ^{2+}$, the metal rods $X$ and $Y$ are inserted (at $298 K$ ) and connected by a conducting wire. This resulted in dissolution of $X$. The correct combination(s) of $X$ and $Y$, respectively, is (are)
(Given: Gas constant, $R =8.314 J K ^{-1} mol ^{-1}$,
Faraday constant, $F =96500 C mol ^{-1}$ )
$(A)$ $Cd$ and $Ni$ $(B)$ $Cd$ and $Fe$ $(C)$ $Ni$ and $Pb$ $(D)$ $Ni$ and $Fe$
Statement $I :$ The $E ^{\circ}$ value of $Ce ^{4+} / Ce ^{3+}$ is $+1.74 \,V$
Statement $II :$ $Ce$ is more stable in $Ce ^{4+}$ state than $Ce ^{3+}$ state.
In the light of the above statements, choose the most appropriate answer from the options given below
$\mathrm{A}+\mathrm{B} \rightarrow \mathrm{C}$
$\text { rate }=\mathrm{k}[\mathrm{A}]^{1 / 2}[\mathrm{~B}]^{1 / 2}$
The reaction is initiated by taking $1 \mathrm{M}$ concentration $A$ and $B$ each. If the rate constant $(k)$ is $4.6 \times 10^{-2} \mathrm{~s}^{-1}$, then the time taken for $\mathrm{A}$ to become $0.1 \mathrm{M}$ is . . . . . . . . . . sec. (nearest integer)