…A… are formed when atoms of different elements combine in a …B… ratio. Here, A and B refer to — Mole Concept and Some Basic Concepts of Chemistry Chemistry Question

💡 Solution & Explanation

# Solution **Understanding the Definition:** The statement describes what forms when atoms of different elements combine in a specific ratio. **Identifying A and B:** - **A** = **Compounds** — These are substances formed by chemical combination of two or more different elements in a definite proportion by mass. - **B** = **Definite** (or **Fixed**) — Compounds always form when elements combine in a definite/fixed ratio, which is why they have consistent chemical formulas like $H_2O$, $NaCl$, $CO_2$, etc. **Why This is Correct:** The fundamental definition of a compound requires: 1. Atoms of **different elements** (not just one element) 2. Combined in a **definite ratio** (the ratio is constant and characteristic for each compound) For example, water is always $H_2O$ (2 hydrogen : 1 oxygen), never $H_3O$ or $HO$. This fixed ratio is what makes it a compound and distinguishes it from mixtures, which can have variable compositions. **Answer:** A = **Compounds**; B = **Definite**