What is the empirical formula of a compound composed of 3.25% hydrogen and 19.36% carbon and 77.39% oxygen by mass

Can someone me with 3 and 4 plz. this is for masteries test.

How many moles of lead are in 1.50 x 10^12 atoms of lead? could you explain the answer as well and not just give it to me i am refreshing for finals and i need to know how to do it

Phosphorous can form an ion called phosphide, which has the formula p3−. this ion can form an ion called phosphide, which has the formula p3−. this ion properties very similar to those of pforms when a phosphorus atom loses three protonsis called a cationcontains 18 electrons