which rule for assigning oxidation numbers is correct?\no hydrogen is usually -1.\no oxygen is usually…

which rule for assigning oxidation numbers is correct?\no hydrogen is usually -1.\no oxygen is usually -2.\no a pure group 1 element is +1.\no a monatomic ion is 0.

which rule for assigning oxidation numbers is correct?\no hydrogen is usually -1.\no oxygen is usually -2.\no a pure group 1 element is +1.\no a monatomic ion is 0.

Answer

Brief Explanations:

  1. Hydrogen usually has an oxidation number of +1 in most compounds (except in metal hydrides where it is - 1).
  2. Oxygen usually has an oxidation number of -2 in most compounds (except in peroxides where it is -1 and in OF₂ where it is +2).
  3. A pure element has an oxidation number of 0, so a pure group 1 element has an oxidation number of 0, not +1.
  4. The oxidation number of a monatomic ion is equal to its charge, not 0.

Answer:

Oxygen is usually -2.