Questions

I am black gold i.e charcoal. It is black when it is not used and when using it is red due to fire and when used it is in grey color as it becomes ash. 

The acid used in lead storage cells is Sulphuric acid. They are used car batteries. Lead-acid batteries are capable of being recharged, which is important for their use in cars.

The one word substitution for Of outstanding significance is monumental which has a meaning of great in importance, in size or any such characteristic.

Kernel follows Round Robin scheme choosing a swap device among the multiple swap devices in Unix System V.