Principle of column chromatography
In normal column chromatography, the stationary phase (usually silica/alumina) is polar. Hence:

• More polar compounds interact more strongly with the stationary phase.
• So they move more slowly and stay longer in the column.
• Less polar compounds move faster and elute first.

Interpreting the figure
In a chromatography column, the band that is lowest in the column comes out first, and the band that is highest remains longer.

From the given figure (with bands labeled $a$, $b$, $c$), the usual interpretation is:

• $a$ is lowest $Rightarrow$ comes out first
• $b$ is in the middle $Rightarrow$ comes out after $a$
• $c$ is highest $Rightarrow$ comes out last

Therefore, polarity order is: $c > b > a$ where $c$ is most polar and $a$ is least polar.

Check each statement

A. Compound $c$ is more polar than $a$ and $b$
This is correct, because $c$ stays highest in the column and hence is retained most strongly.

B. Compound $a$ is least polar
This is correct, because $a$ moves fastest and reaches the bottom first.

C. Compound $b$ comes out of the column before $c$ and after $a$
This is correct, because the elution order is: $a \to b \to c$

D. Compound $a$ spends more time in the column
This is incorrect, because $a$ is least polar and hence spends the least time in the column.

Incorrect statements
Only statement D is incorrect.

Compare with the given options
None of the options exactly says “D only”.
The stored correct answer is D = A, B and C only are incorrect, but from chromatography principles that is not possible because A, B, and C are all correct.

Hence the stored answer appears inconsistent with the chemistry concept.