Correct Answer: 120

Solution : The current ratio of boys to girls in the school is 7 : 5.
This means that out of every 12 students (7 boys + 5 girls), 7 are boys and 5 are girls.
The number of boys and girls in the school is 720.
Number of boys = $\frac{7}{12}×720 = 420$
Number of girls = $\frac{5}{12}×720 = 300$
To make the ratio of boys to girls 1 : 1, the number of girls should be equal to the number of boys.
Additional girls needed = Number of boys – Number of girls = 420 – 300 = 120
Hence, the correct answer is 120.