Which one of the following cities is nearest to the equator?

Singapore is nearest to the Equator. Singapore’s latitude is about 1.4° N (roughly 150–160 km north of 0° latitude) according to lists of capitals by latitude [1]. The other options lie appreciably farther: Jakarta is around 6.2° S (several hundred kilometres south), Colombo about 6.9° N, and Manila roughly 14.6° N, so each is multiple degrees — and many hundreds to over a thousand kilometres — from the Equator. Textbook atlas exercises also single out Singapore as a place for estimating distance from the Equator, reflecting its close proximity [2]. Hence, among the four cities listed, Singapore is the closest to the Equator.

Sources

1. [1] https://en.wikipedia.org/wiki/List_of_national_capitals_by_latitude
2. [2] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 2: The Earth's Crust > Latitude > p. 10