which rule for assigning oxidation numbers is correct? hydrogen is usually -1. oxygen is usually -2. a pure…

Answer:

Oxygen is usually -2.

Explanation:

Step1: Analyze hydrogen rule

Hydrogen is usually +1 in compounds (except in metal hydrides where it is - 1). So "Hydrogen is usually -1" is incorrect.

Step2: Analyze oxygen rule

Oxygen has an oxidation number of -2 in most compounds. This is a common - used rule. So "Oxygen is usually -2" is correct.

Step3: Analyze group 1 element rule

A pure group 1 element has an oxidation number of 0 (in its elemental state), not +1. So "A pure group 1 element is +1" is incorrect.

Step4: Analyze monatomic - ion rule

The oxidation number of a monatomic ion is equal to its charge, not 0. So "A monatomic ion is 0" is incorrect.