In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these have physical and chemical properties resembling calcium?

Because calcium (Ca) has a 20 atomic number(Z),

the Electronics configuration is  1s²,2s², 2p⁶,3s²,3p⁶,4s².

its electronic arrangement is 2, 8, 8, 2.

Calcium, therefore, has two valence electrons.

The element with atomic number 12 has an electrical configuration is 1s²,2s², 2p⁶,3s²,

Its electronic arrangement is 2,8.2.

The element that most closely resembles calcium has two valence electrons.