What is chargeable income?

Take into example someone earning 2.5k per mth (before CPF). Which of these are chargeable?

a. 2,500 x 12?
b. [(2,500 + employer CPF contributions) x 12] + bonus
c. [(80% of 2,500 + employer CPF contribtution) x 12] + bonus
d. other combinations

Thanks!