With which mode heat transfers in solids?

Explanation

**Step-by-Step Solution:**

1. **Understanding Heat Transfer Modes**: Heat can be transferred in three primary modes: conduction, convection, and radiation. Each mode has specific characteristics that determine its applicability in different states of matter.

2. **Identifying the Mode in Solids**: In solids, the primary mode of heat transfer is conduction. This is because the molecules in a solid are closely packed and fixed in their positions.

3. **Reason for Conduction**: In conduction, heat is transferred through the vibration of molecules. When one part of a solid is heated, the molecules in that area gain energy and start to vibrate more vigorously. These vibrations are then passed on to adjacent molecules, transferring heat through the solid.

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