What is the percentage atom economy when the formula weight of the desired product is $65 \text{ u}$ and the sum of the formula weights of all reactants is $130 \text{ u}$ (in $\%$)?

Hydrogen gas is prepared in the laboratory by reacting dilute $HCl$ with granulated zinc. The following reaction takes place: $Zn + 2HCl \to ZnCl_2 + H_2$. Calculate the volume of hydrogen gas liberated at $STP$ when $32.65 \ g$ of zinc reacts with $HCl$. ($1 \ mol$ of a gas occupies $22.7 \ L$ volume at $STP$; atomic mass of $Zn = 65.3 \ u$).

What is $\Delta n$ for the combustion of $1 \ mole$ of benzene,when both the reactants and the products are in the gaseous state at $298 \ K$?

Calculate the volume of $H_2$ gas kept at $STP$ if it contains as many $H$ atoms as in $98 \ g$ of $H_3PO_4$. (Atomic mass of $P = 31 \ u$) (in $L$)

One litre oxygen gas at $STP$ will weigh $.................. \ g$

$H_2$ evolved at $STP$ on complete reaction of $27 \ g$ of Aluminium with excess of aqueous $NaOH$ would be $............ \ L$