Which of the Following Atoms Contains the Largest Number of Neutrons

Which of the following atoms contains the largest number of neutrons?

A) ${ } _ { 20 } ^ { 42 } \mathrm { Ca }$
B) ${ } _ { 19 } ^ { 39 } \mathrm {~K}$
C) ${ } _ { 17 } ^ { 37 } \mathrm { Cl }$
D) ${ } _ { 19 } ^ { 41 } \mathrm {~K}$
E) ${ } _ { 18 } ^ { 42 } \mathrm { Ar }$