What pressure would be required to compress 7.75 litres of hydrogen at 1atmospheric pressure to 5 litres?(1atm=760mm,Hg=760 torrant)

Answer 1

P
1
V
1
=
P
2
V
2
, now
P
1
=
1
⋅
a
t
m
, and so we solve for
P
2
:
P
2
=
P
1
V
1
V
2
=
1.00
⋅
L
×
1
⋅
a
t
m
0.050
⋅
L
=
?
?
a
t
m

Answer 2

This will be easier to read.
Use P1V1 = P2V2
P1 = 1 atm
V1 = 7.75 L
P2 = ?
V2 = 5 L
This assumes T does not change.