Hot water cools from $60\,^{\circ}C$ to $50\,^{\circ}C$ in the first $10\,min$ and to $42\,^{\circ}C$ in the next $10\,min$. The temperature of the surrounding is ......... $^{\circ}C$.

In the circuit shown in the figure,the current $I$ is: (in $\,A$)

Select the incorrect order.

The correct order of acidic strength of the major products formed in the given reactions is:
$A.$ $PhNH_2$ $\xrightarrow[\substack{\text{(2) } CuCN \\ \text{(3) } H_3O^{+} / \Delta}]{\text{(1) } NaNO_2 + HCl \left( < 5^{\circ} C \right)} [A]$
$B.$ $CH_3CH_2CHO \xrightarrow[\Delta]{\left[ Ag \left( NH_3\right)_2\right]^{+}, OH^{-}} [B]$
$C.$ $CH_4 + O_2 \xrightarrow[\text{(ii) } Na_2Cr_2O_7 / H^{+}]{\text{(i) } Mo_2O_3} [C]$
$D.$ $PhCH_2MgBr + CO_2 \xrightarrow[H_3O^{+}]{\text{Dry ether}} [D]$
Choose the correct answer from the options given below:

The cosine of the angle $A$ of the triangle with vertices $A(1, -1, 2)$, $B(6, 11, 2)$, and $C(1, 2, 6)$ is:

Which of the following oxoacids of phosphorus has the lowest oxidation state of phosphorus?