What is the oxidation number of o in po4^3-? a. 0 b. -1 c. -2 d. -3 e. none of the above

Iknow the answer is a but i don't know why

What is the result of multiplying (2.5 × 1010) × (2.0 × 10-7)? a. 5.0 × 103 b. 5.0 × 10-3 c. 5.0 × 1017 d. 5.0 × 10-17

If oil spills continue, all of the following should be expected except (2 points) death of aquatic life. polluted groundwater. decreased soil productivity. increased global temperatures.