The moles of methane required to produce $$81$$ g of water after complete combustion is ______ $$\times 10^{-2}$$ mol. [nearest integer]

We need to find the moles of methane required to produce 81 g of water after complete combustion.

The balanced equation for the combustion of methane is $$CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$$.

The moles of $$H_2O$$ produced are $$\frac{81}{18} = 4.5$$ mol.

According to the balanced equation, 1 mol of $$CH_4$$ yields 2 mol of $$H_2O$$, so the moles of $$CH_4$$ required are $$\frac{4.5}{2} = 2.25$$ mol.

Writing this in the specified format gives $$2.25$$ mol = $$225 \times 10^{-2}$$ mol.

Therefore, the answer is 225.