$A$ spherical ball of radius $7 \ cm$ contains $56 \ w\%$ iron. Find out the number of moles of iron present approximately in the ball (in $.1$)? $(d = 1.4 \ g \ cm^{-3}; \text{atomic mass} = 56 \ g \ mol^{-1})$

Consider the reaction shown below where $6.1 \,g$ of benzoic acid is used to obtain $7.8 \,g$ of $m$-bromobenzoic acid. The percentage yield of the product is ....... .
(Round off to the Nearest integer) [Given : Atomic masses : $C = 12.0 \,u, H = 1.0 \,u, O = 16.0 \,u, Br = 80.0 \,u$]

When $CO_2\,(g)$ is passed over red hot coke,it partially gets reduced to $CO\,(g).$ Upon passing $0.5\,L$ of $CO_2\,(g)$ over red hot coke,the total volume of the gases increases to $700\,mL.$ The composition of the gaseous mixture at $STP$ is

The normality of $2 \ M$ sulphuric acid is: (in $N$)

Zinc reacts with hydrochloric acid to give hydrogen and zinc chloride. The volume of hydrogen gas produced at $STP$ from the reaction of $11.5 \ g$ of zinc with excess $HCl$ is $.......... \ L$ (Nearest integer) (Given: Molar mass of $Zn$ is $65.4 \ g \ mol^{-1}$ and Molar volume of $H_2$ at $STP = 22.7 \ L$)

When $10 \ mol$ of $SO_2$ and $15 \ mol$ of $O_2$ are mixed and passed over a catalyst,$8 \ mol$ of $SO_3$ is formed. How many moles of $SO_2$ and $O_2$ remain unreacted?