Who developed the theory of combustion as a chemical reaction with oxygen in the 18th century, that excluded phlogiston theory?

Correct — B. Antoine Lavoisier showed in the 1770s that burning is a substance combining with oxygen from the air, not the escape of a fire-stuff called phlogiston.

His instrument was the balance. Weighing reactants and products in closed vessels, he found that metals gain weight when they burn — impossible if burning released something.

He named oxygen, redefined combustion as a reaction with it, and left the phlogiston theory unusable → option (b).

Why the others are wrong

• (a)
  Friedrich Wöhler — Wöhler belongs to the 19th century. His landmark was synthesising urea from an inorganic salt in 1828, which broke the wall between organic and inorganic chemistry. Combustion had been settled decades before he began.
• (c)
  Robert Boyle — Boyle belongs to the 17th century, before phlogiston had even been named. He is remembered for the pressure-volume law and for pushing chemistry away from alchemy, not for explaining burning.
• (d)
  Johann Becher — Becher is on the other side of this argument. His terra pinguis, an oily earth supposedly released when things burn, is the idea Stahl renamed phlogiston and the idea Lavoisier's weighings destroyed.

The phlogiston theory held that combustible bodies contain a substance released on burning. It came from Johann Joachim Becher's terra pinguis and was developed and named by Georg Ernst Stahl.

It failed on a measurement. A metal that burns leaves a heavier residue, so burning cannot be a loss. Lavoisier's careful weighing turned that anomaly into a new theory: combustion is combination with oxygen, and nothing is created or destroyed in the process.

That second half is the law of conservation of mass, which is why Lavoisier is called the father of modern chemistry.

Key facts

• Lavoisier explained combustion as the combination of a substance with oxygen, replacing the phlogiston theory.
• He is credited with naming oxygen and with the law of conservation of mass.
• The phlogiston theory came from Johann Joachim Becher's terra pinguis and was developed by Georg Ernst Stahl.
• Lavoisier's Traité Élémentaire de Chimie of 1789 is treated as the first modern chemistry textbook.

Common traps

• Picking Becher because his name is attached to the phlogiston story, when the item asks who ended it.
• Treating Boyle as a general-purpose answer for any early chemistry question.

No directly related past PYQ was found.