Answer: -
1 mol
Explanation: -
Number of moles of Sulphur S = 7
Number of moles of O2 = 9
The balanced chemical equation for the reaction is
2S (s)+3 O2 (g)→2SO3(g)
From the above reaction we can see that
3 mol of O2 react with 2 mol of S
9 mol of O2 will react with

= 6 mol of S
Unreacted S = 7 - = 1 mol.
If a reaction vessel initially contains 7 mol S and 9 mol O2
1 mole of s will be in the reaction vessel once the reactants have reacted as much as possible
Answer:
(a) boiling point
(d) density at a given temperature and pressure.
Explanation:
Isomers are compounds that have the same molecular formula but different structural formulas. They differ in chemical and physical properties depending on the type of isomerism displayed by the compounds.
The compounds stated here are structural or constitutional isomers hence they possess different boiling points and densities at a given temperature and pressure owing to structural differences in the molecules.
Since they have the same molecular formula, they must yield the same result during combustion analysis and they must have the same molecular weight.
D. Changes
Hope this helps :)