What is the formula for this compound? 1 atom of copper, 1 atom of sulfur, 4 atoms of oxygen

Which of these conditions most likely produces an unstable isotope?

Define dew point. i am writing this part to be able to ask the question

For the reaction shown, find the limiting reactant for each of the following initial amounts of reactants. 4al(s)+3o2(g)→2al2o3(s) a) 1 molal, 1 mol o2 b) 4 molal, 2.6 mol o2 c) 16 molal, 13 mol o2 d) 7.4 molal, 6.5 mol o2