The correct answer is (a). A square of side 10 cm has a perimeter of $4 \times 10 = 40$ cm. A rectangle of sides 12 and 9 cm has a perimeter of $2 \times 12 + 2 \times 9 = 42$ cm. A circle of radius 7 cm has a perimeter of $2 \pi r = 2 \pi \times 7 = 44$ cm. A rhombus of sides 9 cm has a perimeter of $4 \times 9 = 36$ cm. Therefore, the square has the longest perimeter.
A square is a four-sided figure with all sides of equal length and all angles of equal measure (90 degrees). A rectangle is a four-sided figure with opposite sides of equal length and opposite angles of equal measure. A circle is a round figure with all points on the circumference equidistant from the center. A rhombus is a four-sided figure with opposite sides of equal length and opposite angles of equal measure, but the angles at the vertices need not be 90 degrees.
The perimeter of a figure is the total length of all its sides. The perimeter of a square is $P = 4s$, where $s$ is the side length. The perimeter of a rectangle is $P = 2l + 2w$, where $l$ is the length and $w$ is the width. The perimeter of a circle is $P = 2\pi r$, where $r$ is the radius. The perimeter of a rhombus is $P = 4a$, where $a$ is the side length.
In this case, the square has a side length of 10 cm. The rectangle has a length of 12 cm and a width of 9 cm. The circle has a radius of 7 cm. The rhombus has a side length of 9 cm.
The perimeter of the square is $P = 4 \times 10 = 40$ cm. The perimeter of the rectangle is $P = 2 \times 12 + 2 \times 9 = 42$ cm. The perimeter of the circle is $P = 2\pi \times 7 = 44$ cm. The perimeter of the rhombus is $P = 4 \times 9 = 36$ cm.
Therefore, the square has the longest perimeter.