If 21 ml of gas is subjected to a temperature change from 10.0°c to 120°c and a pressure change from 1.0 atm to 15 atm, the new volume is

After the change of temperature and pressure-> the number of moles of the gas is still the same.
n1=P1*V1/RT1
n2=P2*V2/RT2
R=0.082 constant... you can cancel it out
n1=n2
10C=10+273.15K=283.15K
120c=120+273.15k=393.15
P1*V1/T1=P2*V1/T2
1*0.021/283.15=15*V2/393.15
V2=1.943*10^-3 L = 1.943ml

B.1 - hydrogren-1 can only mean there is 1 neutron. it's obvious there is 1 proton or else it wouldn't be hydrogen, so they wouldn't put a number after it unless they were indicating the number of neutrons