For a first order reaction the concentration of reactant was reduced from $0.03 \mathrm{molL}^{-1}$ to $0.02 \mathrm{molL}^{-1}$ in 25 min . What is its rate (in $\mathrm{molL}^{-1} \mathrm{~s}^{-1}$ )?
' $X$ ' is a protecting colloid. The following data is obtained for preventing the coagulation of 10 mL of gold sol to which 1 mL of $10 \% \mathrm{NaCl}$ is added. What is the gold number of ' $X$ '?
$$ \begin{array}{ccl} \hline \text { Expt No. } & \begin{array}{c} \text { Weight of } X \text { (in mg) } \\ \text { added to gold sol } \end{array} & \text { Coagulation } \\ \hline 1 & 24 & \text { Not prevented } \\ \hline 2 & 23 & \text { Not prevented } \\ \hline 3 & 26 & \text { Prevented } \\ \hline 4 & 27 & \text { Prevented } \\ \hline 5 & 25 & \text { Prevented } \\ \hline \end{array} $$
The reactions which occur in blast furnace at $500-800 \mathrm{~K}$ during extraction of iron from haematite are
i. $3 \mathrm{Fe}_2 \mathrm{O}_3+\mathrm{CO} \longrightarrow 2 \mathrm{Fe}_3 \mathrm{O}_4+\mathrm{CO}_2$
ii. $\mathrm{Fe}_2 \mathrm{O}_3+3 \mathrm{C} \longrightarrow 2 \mathrm{Fe}+3 \mathrm{CO}$
iii. $\mathrm{Fe}_3 \mathrm{O}_4+4 \mathrm{CO} \longrightarrow \mathrm{Fe}+4 \mathrm{CO}_2$
iv. $\mathrm{Fe}_2 \mathrm{O}_3+\mathrm{CO} \longrightarrow 2 \mathrm{FeO}+\mathrm{CO}_2$