Correct answer: (b) 7 : 9
The distance covered in the nth second of free fall is given by the formula: Sn = u + (1/2)g(2n - 1). For the 4th second, S4 = (1/2)g(2×4 - 1) = (1/2)g(7). For the 5th second, S5 = (1/2)g(2×5 - 1) = (1/2)g(9). The ratio is S4 : S5 = 7 : 9.