Which substance causes the liver to produce massive amounts of acid when ingested?

The liver produces massive amounts of acid when methanol is ingested due to its metabolism into toxic byproducts. When methanol is metabolized in the liver, it is converted first to formaldehyde and then to formic acid. The accumulation of formic acid can lead to metabolic acidosis, which is a severe condition characterized by an excess of acid in the body. This reaction is significant because it disrupts the body's normal pH balance, leading to potentially life-threatening complications.

In contrast, other substances listed, such as isopropanol, hydrocarbons, and cyanide, do not produce massive amounts of acid through liver metabolism. Isopropanol is metabolized to acetone, hydrocarbons can lead to various toxic effects without significantly affecting acid levels in the blood, and cyanide primarily inhibits cellular respiration rather than causing acid production. Therefore, methanol's specific metabolic pathway and resultant acid production make it the key substance mentioned in the question.