MCQ
Calculate atomic number of $A$ and $B$ respectively


- A$71, 72$
- B$58, 72$
- ✓$57, 72$
- D$57, 71$

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Given : $K_b(H_2O) = 0.51\, Kkg \,mol^{-1}$
$N_A = 6 × 10^{23}$
$[Li = 7, \,\,Na = 23$, $K = 39,\,\, Rb = 85.5$ , $Cs = 133, \,\,Cl = 35.5]$
$Fe ^{2+}( aq )+ S ^{2-}( aq ) \rightleftharpoons FeS ( s )$
When equal volumes of $0.06 M Fe ^{2+}( aq )$ and $0.2 M S ^{2-}( aq )$ solutions are mixed, the equilibrium concentration of $Fe ^{2+}$ (aq) is found to be $Y \times 10^{-17} M$. The value of $Y$ is. . . . .