Based on the chemical equation, 4 moles of lithium reacts with 1 mole of oxygen to produce 2 moles of lithium oxide.
First of all you need to find 1 mole of Lithium by diving 1.68 mol by 4 and the answer should be 0.42 mol. To calculate the no. of moles of lithium oxide, you've to multiply 0.42 mol by 2. Hence the answer, 0.84 mol.