The answer is (3) I-131 and P-32. They both have β- decay mode and with half-lives greater than hour. You can get these half-lives and decay mode from table N selected radioisotopes.
<span>PV=nRT= a universal constant
For any condition
P1V1/n1T1=R
and
P2V2/n2T2=R
i.e
P1V1/n1T1=P2V2/n2T2
Becomes
V1/n1=V2/n2
rearranging and solving
V2=V1X(n2/n1)= 750 mLx((0.65+0.35)/(0.65))=1200ml=1.2L...2 sig figs</span>