What is the value of percent atom economy when an organic compound of formula weight $75 \ u$ is obtained from reactants having sum formula weight $225 \ u$?

For per gram of reactant,the maximum quantity of $N_2$ gas is produced in which of the following thermal decomposition reactions? (Given: Atomic wt. : $Cr = 52 \ u, Ba = 137 \ u$).

$4.0 \,g$ of $NaOH$ are contained in one decilitre of solution. Its molarity would be ......... $M$.

An ideal gas mixture of $C_2H_6$ and $C_2H_4$ occupies a volume of $28 \ L$ at $1 \ atm$ and $273 \ K$. This mixture reacts completely with $128 \ g$ of $O_2$ to produce $CO_2$ and $H_2O_{(l)}$. What is the mole fraction of $C_2H_4$ in the mixture?

$12 \ g$ of $Mg$ (atomic mass $24$) will react completely with acid to give:

$10 \ mL$ of conc. $H_2SO_4$ $(18 \ M)$ is diluted to $1 \ L$. The approximate strength of the dilute acid is $........... \ N$.