Identify the correct statements(s) :

• Correct answer
  A

  The oxidation number of Cr in $\mathrm{CrO}_5$ is +6
• Correct answer
  B

  $\Delta \mathrm{H}\gt\Delta \mathrm{U}$ for the reaction $\mathrm{N}_2 \mathrm{O}_4(\mathrm{~g}) \rightarrow 2 \mathrm{NO}_2(\mathrm{~g})$, provided both gases behave ideally
• C

  pH of $0.1(\mathrm{~N}) \mathrm{H}_2 \mathrm{SO}_4$ is less than that of $0.1(\mathrm{~N}) \mathrm{HCl}$ at $25^{\circ} \mathrm{C}$
• D

  $\left(\frac{R T}{F}\right)=0.0591$ volt at $25^{\circ} \mathrm{C}$

Solution

$\begin{aligned} & \text { B: } \quad \mathrm{N}_2 \mathrm{O}_4(\mathrm{~g}) \rightarrow 2 \mathrm{NO}_2(\mathrm{~g}) \\ & \therefore \Delta \mathrm{n}_{\mathrm{g}}=2-1=1\end{aligned}$ and from $\Delta H=\Delta U+\Delta n_g R T ; \Delta H\gt\Delta U$ C: For $0.1 \mathrm{~N} \mathrm{HCl}, \mathrm{pH}$ is 1 $\mathrm{N}_{\mathrm{H}_2 \mathrm{SO}_4}=0.1 \quad \therefore\left(\mathrm{H}^{+}\right)=0.1 \mathrm{~N} \quad \mathrm{~N}_{\mathrm{HCl}}=0.1 \quad \therefore\left(\mathrm{H}^{+}\right)=0.1 \mathrm{~N}$ Since both contains same concentration of $\mathrm{H}^{+}$ion, hence have same pH D : $\frac{2.303 \mathrm{RT}}{\mathrm{F}}=0.0591$ at $25^{\circ} \mathrm{C}$

Hence, the correct answer is options: 'A', 'B'.