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?

Explanation

An element in the periodic table which is surrounded by four other elements can be regarded as the central element of one horizontal row ( period ) and one vartical column group ) .
The three element of the horizontal row have consecutive atomic numbers and hence lie in the same period. On the other hand the three elements of the vertical column do not have consecutive atomic numbers adn hence lie in the same group. For example the element calcium with atomic number 20 is surrounded by four element with atomic number 12, 19 , 21 and 38. Thus the atomic number 20 is surrounded which lie in the same group are 12, 20 and 38. Therefore the physical and chemical properties of calcium resemble with those of the elements having atomic numbers 12 and 38.