1
COMEDK 2025 Evening Shift
MCQ (Single Correct Answer)
+1
-0
An aqueous solution of volume V ml contains a non-volatile solute of unknown mass $W_B \mathrm{~g}$ and molar mass $M_B \mathrm{~g} / \mathrm{mol}$. If the Osmotic pressure of the solution is 1.013 bar, which one of the following is the mathematical expression to be used to calculate $W_B$ ?
A
$W_B=\frac{\pi \mathrm{M}_{\mathrm{B}} V}{760 * \mathrm{RT} * 1000}$
B
$W_B=\frac{\pi \mathrm{M}_{\mathrm{B}} V 1000}{76 \mathrm{RT}}$
C
$W_B=\frac{\pi \mathrm{M}_{\mathrm{B}} V}{\mathrm{RT}}$
D
$W_B=\frac{\pi \mathrm{M}_{\mathrm{B}} V}{1000 \mathrm{RT}}$
2
COMEDK 2025 Evening Shift
MCQ (Single Correct Answer)
+1
-0
The ratio of $\mathrm{N}_2$ and $\mathrm{O}_2$ gases in the atmosphere is $4: 1$. The ratio of the mole fractions of the dissolved gases $\mathrm{N}_2$ : $\mathrm{O}_2$ in rain water will be approximately ........ (At $293 \mathrm{~K}, \mathrm{~K}_{\mathrm{H}}$ for Nitrogen and Oxygen in kbar units are 76.48 and 34.86 respectively.)
A
$3: 1$
B
$2: 1$
C
$4: 1$
D
$1: 4$
3
COMEDK 2025 Evening Shift
MCQ (Single Correct Answer)
+1
-0

Identify the correct coefficients (a), (b), (c) and (d) in the following equations

i) $\quad \mathrm{xMnO}_4^{--}+$(a) $\mathrm{SO}_3{ }^{2-}+$ (b) $\mathrm{H}^{+} \cdots \longrightarrow \mathrm{xMn}^{2+}+$ (a) $\mathrm{SO}_4{ }^{2-}+$ (c) $\mathrm{H}_2 \mathrm{O}$

ii) (c) $\mathrm{S}_2 \mathrm{O}_3{ }^{2-}+$ (d) $\mathrm{MnO}_4^{-}+\mathrm{H}_2 \mathrm{O} \cdots \rightarrow$ (d) $\mathrm{MnO}_2+$ (b) $\mathrm{SO}_4{ }^{2-}+\mathrm{xOH}^{-}$

A
$(a)=3$ (b) $=8$ $(c)=6$ $(d)=6$
B
$(a)=5$ (b) $=6$ $(c)=3$ $(\mathrm{d})=8$
C
(a) $=2$ (b) $=8$ $(c)=4$ $(\mathrm{d})=4$
D
$(a)=2$ (b) $=6$ $(c)=6$ $(d)=5$
4
COMEDK 2025 Evening Shift
MCQ (Single Correct Answer)
+1
-0
The decomposition of $\mathrm{PH}_3$ follows first order kinetics. The time required for $3 / 4^{\text {th }}$ of $\mathrm{PH}_3$ to decompose is 75.76 s . Calculate the fraction of original amount of $\mathrm{PH}_3$ which will remain after 2.0 minutes.
A
0.354
B
0.111
C
0.954
D
0.898
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