What is the chemical formula of Tin $(IV)$ oxide?

$20 \, mL$ of $1 \, N \, KMnO_4$ solution reacts with $20 \, mL$ of oxalic acid solution. The weight of oxalic acid crystals $(H_2C_2O_4 \cdot 2H_2O)$ in the $1 \, N$ solution is . . . . . . $g$.

$18 \ L$ mixture of $N_2$ and $H_2$ gives maximum $6 \ L$ of $NH_3$ at same temperature and pressure. What will be the ratio of $N_2$ and $H_2$ initially taken?

$60 \ mL$ $NaOH$ solution is required for complete neutralization of $0.98 \ g$ orthophosphoric acid. The concentration of $NaOH$ solution is ............. $M$.

When a $1.0 \, g$ mixture of $NaHCO_3$ and $Na_2CO_3$ is heated at $150^{\circ}C$,$112.0 \, mL$ of $CO_2$ is produced at $STP$. Calculate the percentage of $Na_2CO_3$ in the mixture. $(Na = 23, C = 12, O = 16)$

How much solid oxalic acid (Molecular weight $126$) has to be weighed to prepare $100 \ mL$ of exactly $0.1 \ N$ oxalic acid solution in water (in $g$)?