$100 \ g$ of a mixture of $NaOH$ and $Na_2SO_4$ is neutralized by $100 \ mL$ of $0.5 \ M \ H_2SO_4$. What is the amount of $Na_2SO_4$ present in the mixture (in $g$)?

The number of electrons in one molecule of urea $(NH_2CONH_2)$ is

In a $20\%$ aqueous solution of $H_2O_2$,the mole fraction of water is $.......$.

Identify the compound formed from elements $X, Y, Z$ having oxidation states $+2, +5, -2$ respectively.

What is the percentage of lead in a lead pencil (in $\%$)?

For the reaction: $N_{2(g)} + 3H_{2(g)} \rightarrow 2NH_{3(g)}$,$\Delta H = -24 \ \text{kcal}$ at $427 \ ^\circ\text{C}$ and $200 \ \text{atm}$. Calculate the magnitude of the internal energy change ($\Delta U$ in $\text{kcal}$),if $168 \ \text{g}$ of $N_2$ gas and $30 \ \text{g}$ of $H_2$ gas are allowed to react completely ($100\%$ reaction yield) to form $NH_3$ gas at $427 \ ^\circ\text{C}$ and $200 \ \text{atm}$.