What is the percent atom economy if the formula weight of reactants and the formula weight of products are $45 \ u$ and $35 \ u$ respectively (in $\%$)?

Two elements $A$ and $B$ form $0.15 \ mol$ of $A_2 B$ and $AB_3$ type compounds. If $0.15 \ mol$ of both $A_2 B$ and $AB_3$ weigh equally,then the atomic weight of $A$ is $...$ times the atomic weight of $B$.

What is the quantity of hydrogen gas liberated when $46 \ g$ sodium reacts with excess ethanol? (Given Atomic mass of $Na = 23$)

The volume of $0.02 \, M$ aqueous $HBr$ required to neutralize $10.0 \, mL$ of $0.01 \, M$ aqueous $Ba(OH)_2$ is $....... \, mL$ (Assume complete neutralization).

For the combustion reaction of $1 \, mol$ of a hydrocarbon $C_xH_y$,the coefficients of $O_2$,$CO_2$,and $H_2O$ involved are respectively:

$1.0 \ g$ of pure calcium carbonate was found to require $50 \ mL$ of dilute $HCl$ for complete reaction. The strength of the $HCl$ solution is given by ........ $N$.