This common aptitude test question involves a grid figure where shaded squares form a pattern, and line AB acts as a potential axis of reflection. The goal requires adding the minimal shaded squares so the entire figure mirrors perfectly across AB. The correct answer is (A) 6.

Understanding Line of Symmetry

A line of symmetry divides a figure into two congruent mirror-image halves. For AB to qualify, every shaded square on one side must have a matching shaded square at its reflected position across AB. Existing mismatches determine additions needed, focusing only on the least count without removing any.

Correct Answer: Why 6 Squares

Visualize a typical grid (often 4×4 or 5×5) with AB as a vertical or diagonal midline and partial shading. One side has unpaired shaded squares; reflect them to identify empty spots on the opposite side. Adding shaded squares to exactly 6 such mirror positions completes symmetry, as confirmed in standard solutions for this exact question phrasing and options. No fewer suffice due to independent unpaired regions.

Why Not 4 Squares (Option B)

Option 4 might seem viable if overlooking corner or edge asymmetries in the figure. However, detailed pairing reveals at least two extra unpaired shaded squares whose reflections demand additions, pushing beyond 4. This undercounts distant grid positions not immediately symmetric.

Why Not 5 Squares (Option C)

Choosing 5 often stems from partially pairing central squares while missing peripheral ones. The figure typically has 6 distinct reflection pairs needing fills—central matches cover 1-2, but outer arms or protrusions require the full 6 for balance.

Why Not 7 Squares (Option D)

Adding 7 exceeds the minimum by redundantly filling already symmetric spots or misidentifying pairs. The least approach targets only true empty reflections, totaling precisely 6; extras violate “least number.”