Hope you could understand.
If you have any query, feel free to ask.
The correct option is C. The amount of MgCl2. we know this because <span>no matter how much you increase KOH, if you dont increase Mgcl2, the amount of Mg(OH)2 remains the same. Hope this works for you</span>
The particles are always in motion but not much and the particles are moving slower because said rock is a solid but if said rock was a gas the particles would move much faster and farther this is due to the gaining and loss of energy (i hope that makes sense)