What are the important elements and compound in Industry?

The answers given are unfortunately innaccurate. an element is something in the periodic table. sulphuric acid for example is not one of them but a combination of two.

The most important element is IRON (Fe) because it is oxidised to make steel which builds almost all our structures.

The most important compound (i.e. product of reaction) is ammonia.
Historically sulphuric acid consumption was used to guage the strength of a country's economy.

The mineral acids (e.g. HCl, H2SO4, HNO3), and gases (e.g. N2, H2, O2) along with sodium, oil and water seem to be the most important.
H2O, the chemists, engineers and workers die without it.
Hydrogen and Carbon
Hydrogen and Oxygen (good old H20, water) without it very little else would be made. Water is used for so much stuff form crystallisation to simple washing most industrial chemistry uses it.
The other thing is Carbon, this gives us our plastics , dyes, pharmaceuticals diamonds, oils and lubricants, means of propulsion and energy etc etc carbon pervades all industries in one form or another
Well there about a hundred different answers to this. Most industrial processes use water H2O but metals such as iron have been very important historically. Nowadays hydrocarbons are used everywhere as fuels. You could make a case for a lot of different elements and compounds.
crude oil