The question can be changed into a new form:
Which element has the most negative electron affinity, or attraction for electrons? halogens have the highest electron affinities, and thus are more attracted to the electrons in the Hydrogen atom than any element in their respective periods.
In this case all the following choices are in the same period, thus Cl or Chlorine is the answer as it is a halogen.
        
             
        
        
        
Answer:
a) K = 5.3175
b) ΔG = 3.2694
Explanation:
a) ΔG° = - RT Ln K
∴ T = 25°C ≅ 298 K
∴ R = 8.314 E-3 KJ/K.mol
∴ ΔG° = - 4.140 KJ/mol
⇒ Ln K = - ( ΔG° ) / RT
⇒ Ln K = - ( -4.140 KJ/mol ) / (( 8.314 E-3 KJ/K.mol )( 298 K ))
⇒ Ln K = 1.671
⇒ K = 5.3175
b) A → B 
∴ T = 37°C = 310 K
∴ [A] = 1.6 M
∴ [B] = 0.45 M
∴ K = [B] / [A]
⇒ K = (0.45 M)/(1.6 M)
⇒ K = 0.28125
⇒ Ln K = - 1.2685
∴ ΔG = - RT Ln K
⇒ ΔG = - ( 8.314 E-3 KJ/K.mol )( 310 K )( - 1.2685 )
⇒ ΔG = 3.2694
 
        
             
        
        
        
Volume of Hydrogen V1 = 351mL 
Temperature T1 = 20 = 20 + 273 = 293 K 
Temperature T2 = 38 = 38 + 273 = 311 K 
We have V1 x T2 = V2 x T1 
So V2 = (V1 x T2) / T1 = (351 x 311) / 293 = 372.56 
Volume at 38 C = 373 ml
        
             
        
        
        
D as the two substances could have close boiling points, so if the temperature is not controlled well, both substances will evaporate.