Use hot water if you want to take the wax off fruits such as apples. The wax is safe to eat or it wouldn't be on there. Keeping hot foods hot and cold foods cold sometimes can take planning, but it's mostly common sense. Don't let foods thaw at room temperature. Your mother may have done this, but don't.
Bacteria can grow in the outer thawed layers while the inside is still frozen.
Thaw food in the refrigerator or in the microwave. An exception is frozen breads, which can be thawed at room temperature. In general, follow the two-hour rule. Don't let prepared foods sit at room temperature for more than two hours. No more than two hours in your car trunk.