Elaborate on the difference in natural occurrences between fission and fusion reactions.

Fission is the division of one atom into two, and fusion is the combination of two lighter atoms into larger one. They are opposing processes and therefore very different.

Hoping that this is what you are looking for.

True, the standard unit for volume is liters which can be represented by either a lower case "l" or a capital "l"

Matter- occupies space and possesses rest massno matter is the opposite