Why does a solid change to a liquid when heat is added

0.2348 grams of pbcl2 used to form 44.0 ml of solution.

When the speed of the bottle is 2 m/s, the average maximum height of the beanbag is m.

Which of the following nuclei would be the least stable a 2 protons, 2 neutrons b 1 proton 1 neutron c 1 proton 3 neutrons d 1 proton 2 neutrons