4. The compound iron sulfide can be formed by filtering b. evaporating heating
a. filtering
C. heating
d. mixing

When iron sulfide is exposed to oxygen it reacts rapidly, releasing large amounts of heat.

Explanation:

i took this from my notes- so whatever aligns with that. sorry if this didnt help but i think its genuinely c heating

on passing the small ampere of electric current through the tube made of ar and hg of cfl generates uv rays which excites the fluorescent and thus emits the high radiation by consumption of just 5- 12 w in comparison to incandescent light which requires more power such as around 40 - 55 w to lighten.

moreover the life span of fluorescent or cfl is around 8000 h whereas the life span of incandescent is around 1200 h

hence, the building installed with incandescent lights bears more electricity bill.