Deduce which nucleus is formed when potassium-40 absorbs an electron.

Use the nuclear equation below and the list of proton (atomic) numbers to help you:

• Argon (Ar): proton number = 18
• Potassium (K): proton number = 19
• Calcium (Ca): proton number = 20

$${}_1^{1}p+{}_{-1}^{0}e⟶{}_0^{1}n$$