Q: 34 (NDA-I/2018)
question_subject:
Science
question_exam:
NDA-I
stats:
0,8,7,8,6,1,0
keywords:
{'formula unit cas04': [0, 0, 0, 1], 'water molecules': [0, 0, 1, 0], 'plaster': [0, 0, 1, 0], 'number': [0, 0, 0, 2], 'paris': [9, 1, 6, 11]}
In plaster of Paris, the chemical formula is CaSO4·2H2O. This means that each formula unit of CaSO4 is associated with two water molecules. In other words, two water molecules are attached or "share" with each formula unit of CaSO4.
So, when we are considering two formula units of CaSO4, the number of water molecules that share with these two formula units would be 2 multiplied by 2, which is equal to 4.
Therefore, the correct answer should be four, not one.
Alert - correct answer should be 4.