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Which sample of matter is classified as a substance?
(1) air (3) milk(2) ammonia (4) seawater


Sagot :

A chemical substance has the characteristics that it cannot be separated by physical  methods. Seawater and milk can be separated by sedimentation, and air has different components depending on other aspects (such as elevation). Only ammonia is a substance. (thus it can have a formula: NH3)