Which of the following octahedral complexes does not exhibit geometric isomerism? ($A$ and $B$ are monodentate ligands.)

The $pK_a$ values of four carboxylic acids are $4.76, 4.19, 0.23$,and $3.41$ respectively. The $pK_a$ value of the strongest carboxylic acid among them is

$A$ die is thrown four times. The probability of getting a perfect square in at least one throw is

The structure of $H_2O_2$ is

The enthalpy change $(\Delta H)$ for the reaction,$N_{2(g)} + 3H_{2(g)} \rightarrow 2NH_{3(g)}$ is $-92.38 \ kJ$ at $298 \ K$. The internal energy change $\Delta U$ at $298 \ K$ is $... \ kJ$.

Which of the following reagents is used in the Gatterman-Koch formylation of arene?