Q.Which of the following pair of elements has similar properties?
a. 13, 31
b. 11, 20
c. 12, 10
d. 21, 33

The modern (long-form) periodic table arranges all 118 known elements into 7 horizontal periods (numbered 1-7) and 18 vertical groups (numbered 1-18, per IUPAC), with each element occupying the box at its period-group intersection. Two additional 14-element rows — the lanthanoid and actinoid series — are placed separately below the main grid, conventionally attached to group 3 of periods 6 and 7. Viewed as a whole, the table's shape divides into four blocks: the two left-hand groups (s-block), the ten central groups (d-block), the six right-hand groups (p …