The separation of two coloured substances was done by paper chromatography. The distances travelled by solvent front, substance A and substance B from the base line are $$3.25 \text{ cm}$$, $$2.08 \text{ cm}$$ and $$1.05 \text{ cm}$$ respectively. The ratio of $$R_f$$ values of A to B is ______ (Answer the nearest integer).

We need to find the ratio of Rf values of substances A and B.

Recall the formula for Rf value

$$R_f = \dfrac{\text{Distance travelled by substance}}{\text{Distance travelled by solvent front}}$$

Calculate Rf for substance A

$$R_f(A) = \dfrac{2.08}{3.25} = 0.64$$

Calculate Rf for substance B

$$R_f(B) = \dfrac{1.05}{3.25} = 0.3231$$

Find the ratio

$$\dfrac{R_f(A)}{R_f(B)} = \dfrac{0.64}{0.3231} = \dfrac{2.08}{1.05} = 1.981$$

Round to the nearest integer

$$\dfrac{R_f(A)}{R_f(B)} \approx 2$$

The answer is 2.