$x$ grams of calcium carbonate was completely burnt in air. The weight of the solid residue formed is $28 \,g$. What is the value of $x$ (in grams)?

$17.0 \ g$ of $NH_3$ completely vaporizes at $-33.42^{\circ}C$ and $1 \ bar$ pressure,and the enthalpy change in the process is $23.4 \ kJ \ mol^{-1}$. The enthalpy change for the vaporization of $85 \ g$ of $NH_3$ under the same conditions is $..... \ kJ$.

$A$ $40 \%$ $HCl$ solution has density $1.2 \ g \ mL^{-1}$. The molarity of the solution is nearly . . . . . . (in $M$)

Element $A$ reacts with oxygen to form a compound $A_2O_3$. If $0.359 \ g$ of $A$ reacts to form $0.559 \ g$ of the compound,the atomic mass of $A$ is:

What mass in $g$ of hydrated oxalic acid $(H_2C_2O_4 \cdot 2H_2O)$ should be added for complete neutralization of $100 \ mL$ of $0.2 \ N \ NaOH$ solution?

$1 \text{ mole}$ of concentrated $HCl$ requires $X \text{ moles}$ of dilute $NaOH$ for neutralization,and $1 \text{ mole}$ of concentrated $H_2SO_4$ requires $Y \text{ moles}$ of dilute $NaOH$. Which of the following relations is true?