Here's the question you clicked on:
Raindrop
How many atoms of hydrogen are found in 8.01 mol of decane, C10H22?
1 mole of decane contains avagadro's number of molecules or 6.023 x 10^23 molecules. So 8.01 moles contains : \[8.01\times 6.023\times 10^{23} molecules\]
But each molecule of decane contains 22 atoms of hydrogen so multiply the above answer by 22 to get the atoms of hydrogen.
I did that and it said I was wrong.
Perhaps you entered your answer in the wrong form or didn't pay attention to significant digits.
I got 1061.37 x 10^23 which would be 1.06 x 10^26
Three significant digits are all we are entitled to.