Recall the basic principle of chromatography

In most common adsorption chromatographic methods like TLC and column chromatography, the stationary phase is polar (for example, silica gel or alumina), and the mobile phase is relatively less polar.

• Polar compounds interact more strongly with the polar stationary phase.
• Non-polar compounds interact less strongly, so they move faster with the mobile phase.

Evaluate option A

Option A says: $R_f$ of a polar compound is smaller than that of a non-polar compound.

In TLC, $R_f = \frac{\text{distance travelled by solute}}{\text{distance travelled by solvent front}}$

Since a polar compound is held more strongly by the polar stationary phase, it travels less distance, so its $R_f$ is smaller.

Therefore, A is correct.

Evaluate option B

Option B says: Non-polar compounds are retained at top and polar compounds come down in column chromatography.

This is the opposite of what happens in normal column chromatography with a polar stationary phase:

• Polar compounds are retained more strongly near the top.
• Non-polar compounds elute first and come down faster.

Therefore, B is incorrect.

Evaluate option C

Option C says: Organic compounds run faster than solvent in the thin layer chromatographic plate.

This is impossible because the solvent front always moves ahead of the solute spots.

By definition, $R_f < 1$ for a normal TLC run, since the solute cannot travel farther than the solvent front.

Therefore, C is incorrect.

Evaluate option D

Option D says: $R_f$ is an integral value.

$R_f$ is a ratio, usually a fractional decimal value between 0 and 1.

It is not necessarily an integer.

Therefore, D is incorrect.

Final conclusion

The only correct statement is: $\boxed{\text{A}}$