in HNO3 the valency of hydrogen is 1 and valency of NO3 is 2 then why it is written HNO3 in place of H2NO3

It is because there are some exceptions in organic chemistry. like carbon-dioxide. the valency of oxygen is 2 and valency of carbon is 4 therefore it should be written as C2H4 but it is written as CO2 it is because carbon and oxygen form covalent bonds and carbon needs 4 atoms to become stable and oxygen 2 therefore carbon shares two atoms of one oxygen atom and one oxygen atom shares two atoms with carbon and carbon shares other two atoms with other oxygen and oxygen shares two atoms with carbon thus two oxygen atoms react with a carbon atom to form CO2 like in the same way HNO3 is an exception. It is in class 10 chemistry

u dont know co2 is correct it is written as c2o4 devide by 2 u get co2

 No you are wrong. CO2 is an exception . You should first learn about covalent bonds. I am not saying that CO2 is wrong i am say why co2 is formed and why not C2h4 is written. You better learn chemistry and thentt alk

Chemistry of class 10. You do not know anything