Please can someone explain the reason Iron has 2 or 3 valence electrons

The electronic configuration of iron is: Ar3d64s2. the two electrons in the 4s orbital are paired, and two of the electrons in the 3d orbitals are paired leaving four unpaired electrons.

Explanation:

we can conclude that the melting point of table salt is above room temperature (it's actually 801 deg c). the melting point of mercury must be below room temperature (- 39 deg c).

chemical digestion occurs in the stomach were hcl and pepsin forms chyme, the mouth in which salivary amylase breaks down starch to form bolus, and the small intestine specifically the duodenum.