What is the ratio of moles of sulfur to moles of sulfur trioxide in
25 +302-->2SO3

It's 2:2

Explanation: you can look at the coefficient stands in front of the chemical

For example if they ask the ratio of oxygen to sulfur trioxide, it would be 3:2 and vice versa vv..

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.