Answer : The mass percentage of hydrogen in hexanal is, 12 %
Explanation: Given,
Molar mass of C = 12 g/mole
Molar mass of H = 1 g/mole
Molar mass of O = 16 g/mole
First we have to calculate the molar mass of hexanal.
Molar mass of hexanal
= 
Now we have to calculate the mass of carbon.
As we now that there are 6 number of carbon atoms, 12 number of hydrogen atoms and 1 number of oxygen atoms.
The mass of hydrogen = 
Now we have to calculate the mass percentage of hydrogen in hexanal.
Formula used :

Now put all the given values in this formula, we get:

Therefore, the mass percentage of hydrogen in hexanal is, 12 %