Given the task definition and input, reply with output. Given a scientific passage and an answer, generate a question for the given answer.

Passage: In chemical equations, reactants and products are represented by chemical symbols and formulas. Numbers called coefficients are placed in front of the symbols and formulas to show how much of each substance is involved in the reaction. Answer: how much is involved in the reaction
What does the coefficient in front of an element in a formula indicate?