The law of photochemical equivalence was given by:

Options

A. Drapper
B. Grauths
C. Einstein
D. Lambert

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the origin of the law of photochemical equivalence. We need to identify which scientist proposed this law.

2. **Options Provided**: The options given are:
- A) Draper
- B) Grothus
- C) Einstein
- D) Lambert

3. **Identifying the Correct Scientist**:
- The law of photochemical equivalence states that for each photon of light absorbed by a chemical system, one molecule is activated for a photochemical reaction.
- This law is also known as the Stark-Einstein law or the second law of photochemistry.

4. **Historical Context**:
- Albert Einstein is credited with formulating this law, which links the absorption of light to the activation of molecules in photochemical reactions.

5. **Conclusion**: Based on the information, the correct answer is option C) Einstein.

**Final Answer**: The law of photochemical equivalence was given by Albert Einstein.

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