b
For A: \(100 gm\) solution \(\rightarrow 2\,gm\) solute \(A\)

\(\therefore \text { Molality }=\frac{2 / M _{ A }}{0.098}\)

For \(B\) : \(100\,gm\) solution \(\rightarrow 8\,gm\) solute \(B\)

\(\therefore \text { Molality }=\frac{8 / M _{ B }}{0.092}\)

\(\because\left(\Delta T _{ B }\right)_{ A }=\left(\Delta T _{ B }\right)_{ B }\)

\(\therefore\) Molality of \(A=\) Molality of \(B\)

\(\therefore \frac{2}{0.098 M _{ A }}=\frac{8}{0.092 M _{ B }}\)

\(\frac{2}{98} \times \frac{92}{8}=\frac{M_{A}}{M_{B}}\)

\(\frac{1}{4.261}=\frac{ M _{ A }}{ M _{ B }}\)

\(\therefore M_{B}=4.261 \times M_{A}\)