$X \ g$ of $Ca$ [atomic mass $= 40$] dissolves completely in concentrated $HCl$ solution to produce $5.04 \ L$ of $H_2$ gas at $STP$. The value of $X$ is closest to

In a chemical reaction, the sum of the formula weights of all reactants is $274 \text{ u}$ and the atom economy is $50\%$. Calculate the formula weight of the desired product. (in $\text{ u}$)

To neutralize $25 \, mL$ of $0.25 \, M$ $Na_2CO_3$ solution,how much volume of $0.5 \, M$ $HCl$ is required? (Note: The reaction is $Na_2CO_3 + 2HCl \rightarrow 2NaCl + H_2O + CO_2$)

What is the percentage atom economy during the conversion of reactant to product if the formula weight of reactants is $246 \ u$ and that of the product is $123 \ u$ (in $\%$)?

The vapour density of a gas is $11.2$. The volume occupied by $11.2 \ g$ of this gas at $N.T.P.$ is ................ $L$

The volume of $0.1 \, M$ $H_2SO_4$ that is needed to completely neutralize $40 \, mL$ of $0.2 \, M$ $NaOH$ is $..... \, mL$.