MCQ practice · SSC Chemistry Board questions · Chapter 6: Concept of Mole and Chemical Counting
How many atoms are there in the phosphate compound of calcium?
Think it through first, then pick an option.
- a 6
- b 11
- c 13
- d 18
Answer and explanation
Correct answer: c 13
Ca₃(PO₄)₂: 3 Ca, 2 P and 8 O, 3 + 2 + 8 = 13 atoms in all.
Why the other options are wrong
- a 6: 6 matches no count here; the O atoms alone are 8. The total is 3 + 2 + 8 = 13.
- b 11: 11 is 3 Ca plus 8 O with the 2 P left out; 3 + 2 + 8 = 13.
- d 18: 18 is too many; the 2 outside the bracket gives 2 × (1 + 4) = 10, plus 3 Ca, 13 in all.
More board questions on this topic
- How many hydrogen atoms are there in 1 mole of water molecules?
- How many atoms are there in one molecule of calcium phosphate?
- The molecular formula H₃PO₄:
Your account is open, so all 30,000+ MCQs from every chapter are yours. Start practising SSC Chemistry →
Want to keep going?
A free account carries you on to the next questions and opens 30,000+ MCQs from every chapter. Join before launch and Chirkut bundles are 60% off.
The ones you missed, worth one more look