Hydrogen reacts with 0.771 g of carbon to form 0.90 g of a compound. what is the mass percent of hydrogen in the compound

In your case, you know that an unknown mass of hydrogen reacts with 0.771 g of carbon to form 0.90 g of hydrocarbon, which is a compound that contains only carbon and hydrogen. 

Use the total mass of the hydrocarbon to determine how many grams of hydrogen reacted with the carbon.

Now, if 0.90 g of this compound contain 0.129 g of hydrogen, it follows that 100 g of this compound will contain.

So, if 100 g of this compound contain 14.33 g of hydrogen, it follows that the mass percent of hydrogen is 14.3%

a saline water is fed to a reverse osmosis unit at flow rate o rotameter connected to reject (retentate) line reads 8 installed in reject and permeate line reads 15.2 milli siemens/cm and 300 micro siemens/com respectively.

the maximum mass of nh3 is nh3 in grams