You have a sample of water that contains the organic compound
c7h12on2 at a concentration of 50
mg/l. the compound can be oxidized by bacteria to form carbon
dioxide, water, and ammonia. how many mg/l of oxygen is needed to
biodegrade the compound? note: determine only carbonaceous
demand.

131.4 mg/L of oxygen is needed to  biodegrade the organic compound.

Explanation:

The chemical reaction will be written as:

Concentration of the organic compound = 50 mg/L

This means that 50 milligrams of organic compound in present in 1 L of the solution.

50 mg = 0.050 g

1 mg = 0.001 g

Moles of organic compound =

According to reaction, 2 moles of organic compound reacts with 23 moles of oxygen gas.

Then 0.0003571 moles of an organic compound will react with:

oxygen gas.

Mass of 0.004107 moles of oxygen gas:

0.004107 mol × 32 g/mol = 0.1314 g = 131.4 mg

131.4 mg/L of oxygen is needed to  biodegrade the organic compound.

it's all four options.