Mountain Bike Chain Keeps Breaking. Use a proper bicycle chain lubricant. In some cases, a dropped chain is a one-off occurrence, but if it continues to happen then there's likely a good reason for it.
It's one of the few chain lubes that can stand up to the worst conditions. Trying to save a couple of $$ on a mountain bike when going offroad will just cost you more and ruin your day eventually.. Flip the bike over and pedal it with one hand, dropping bits of lubricant onto the chain with the other.
I'll try to keep this simple.
Sizing a bike chain can feel like a bit of a process, particularly if it's your first time.
Don't continually break and re-connect the chain. Breaking a chain is rarely an isolated incident and more frequently, it is the sign of a larger issue. Apply a few drops of mineral-based chain oil into each of the links.