Your lawn mower is usually has a 4-cycle engine on it. Some older models had a 2-cycle engine but there are not many of those left so we won’t worry about them.
A 4-cycle engine is designed to work on unleaded gasoline. There are normally 3 or 4 different octane levels of gasoline available. 85, 87, 90 and 93 are very common throughout the country. A lot of people are under the misconception that if they buy 93 octane, their engine will run better when actually the opposite will occur. A higher octane fuel is designed for a higher compression engine. Most lawn mower engines are on the lower scale of compression.
Find the lowest octane rating such as 85 and that will work fine. You could also use non-ethanol fuel to help prevent your carburetor from experiencing problems. Ethanol has been a terrible additive for gasoline engines and especially carburetor engines. Ethanol is alcohol and it attracts moisture and this adds water to your fuel. Water is never good to have in fuel.
Do not put E-85 in your lawn mower gas tank or any other alternative fuels. They will destroy your engine over time. So if you just stick with regular old pump gas, your lawn mower will run like it should.