if 100.0 grams of copper (cu) reacts completely with 25.0 grams of oxygen, how much oxygen will completely react with 140 grams of copper?

35 grams of oxygen

Explanation:

The law of constant proportion or composition states that the elements that combine to form a chemical compound combine in fixed whole number ratios.

Therefore, the ratio of the that make up any pure sample of a given compound are present in the same mass ratio

The given parameters are;

The mass of oxygen that reacts completely with 100 grams of copper, (cu) = 25.0 grams

Therefore;

1 gram of copper completely reacts with 25/100 = 1/4 grams of oxygen

140 grams of copper will completely react with 140 × 1/4 = 35 grams of oxygen

∴ 35 grams of oxygen will completely react with 140grams of copper.

it's all four options.