* Elements: Elements are pure substances that cannot be broken down into simpler substances. Examples include lead (Pb), nitrogen (N), and oxygen (O).

* Mixtures: Mixtures are combinations of two or more substances where each substance retains its own properties. Examples include salt and pepper or sand and water.

* Compounds: Compounds are formed when two or more elements chemically combine in a fixed ratio. The resulting compound has properties that are different from the original elements.

Lead nitrate (Pb(NO₃)₂) is formed by the chemical combination of lead (Pb), nitrogen (N), and oxygen (O) in a specific ratio. It has properties distinct from lead, nitrogen, or oxygen alone.