HELLO HANSA,
you are asking so many doubts i like that and that too your questions are very beautiful
may you get the good success in JEE /NEET
ok i will explain your doubt as follows
moles of solute = 0.2 in 0.8 moles of benzene
so mass of benzene = 0.8X78
so molality = 0.2X1000/0.8X78
= 1.2
so molality = 1.2
THANK YOU VERY MUCH