According to the text, the abundance of formed elements is as follows:

1. Erythrocytes (RBCs): Most abundant, 5 - 5.5 million mm⁻³ .
2. Platelets: 1,50,000 - 3,50,000 mm⁻³ (General knowledge, listed as formed elements in text ).
3. Leucocytes (WBCs): 6000 - 8000 mm⁻³ .

Among WBCs, the order of abundance is:

• Neutrophils: 60-65% (Most abundant WBC)
• Monocytes: 6-8%
• Eosinophils: 2-3%
• Basophils: 0.5-1% (Least abundant)

Therefore, the decreasing order is: Erythrocytes (c) > Platelets (a) > Neutrophils (b) > Monocytes (e) > Eosinophils (d).