In the form of matter where molecules are most closely packed together is solid. In solids, molecules are tightly packed in a fixed arrangement, resulting in a definite shape and volume. This close packing allows for strong interactions and minimal molecular movement, making solids rigid. Examples of solids include metals, salts, and various organic compounds. The arrangement of molecules in solids contrasts sharply with liquids and gases, where molecules have more space to move and are not held in fixed positions.