Answer: Lithium
Explanation: The balanced chemical equation is:

It can be seen, 4 moles of lithium combines with 1 mole of oxygen gas to produce 2 moles of lithium oxide.
Thus 8.4 moles of lithium combines with=
of oxygen gas to produce 4.2 moles of lithium oxide.
As, Lithium limits the formation of product, it is the limiting reagent and Oxygen gas is present in excess, it is called the excess reagent. (4.6-2.1)=2.5 moles of oxygen gas are present in excess.
Answer:
Blue, orange and green
Explanation:
Three different colors are observed from compounds containing different oxidation states of chromium: +2 (blue), +3 (green), and +6 (orange).
The molar mass or As is 74.9g. Start with 281g multiply by (1mol/74.9g) = 3.75 mols
Put what you don’t want on the bottom (in this case grams) so they the u it’s cancel (if you multiply by grams and the divide by grams they cancel. Ultimately leave what you want on the top ( This case mols) then do the math