Correct two-thirds of French students about the old Russian scientist (10)

'correct two-thirds' is the definition.
The definition suggests a singular noun which matches the answer.

'french students about the old russian scientist' is the wordplay.
I cannot really understand how this works, but
'scientist' could be 'mendel' (Mendel is an example) and 'mendel' is located in the answer.
'the old' could be 'ye' (resembles a historical spelling of 'the') and 'ye' is found within the answer.
This explanation may well be incorrect...

'of' is the link.

Can you help me to learn more?