Which one of the following elements will be an isobar of calcium if the atomic number of calcium is 20 and its mass number is 40?

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Q: 31 (CDS-I/2018)

Which one of the following elements will be an isobar of calcium if the atomic number of calcium is 20 and its mass number is 40?

question_subject: 

Science

question_exam: 

CDS-I

stats: 

0,17,24,10,7,7,17

keywords: 

{'isobar': [0, 0, 0, 1], 'elements': [0, 0, 2, 5], 'calcium': [2, 0, 0, 4], 'neutrons': [0, 0, 1, 1], 'element': [0, 0, 0, 1], 'atomic number': [0, 0, 0, 4], 'mass number': [0, 0, 0, 3], 'protons': [0, 0, 0, 1]}

Option 1: This option states that the isobar of calcium has 20 protons and 18 neutrons. However, the atomic number of an element determines the number of protons it has, and since calcium has an atomic number of 20, this option is incorrect.

Option 2: This option suggests that the isobar of calcium has 18 protons and 19 neutrons. Again, the atomic number of calcium is 20, so this option is also incorrect.

Option 3: According to this option, the isobar of calcium has 20 protons and 19 neutrons. However, since calcium has an atomic number of 20, this option is incorrect.

Option 4: This option proposes that the isobar of calcium has 18 protons and 22 neutrons. While the number of protons is different from calcium, the number of neutrons is also different. Therefore, this option is correct, as an isobar of calcium can have a different number of protons and neutrons.

In conclusion, the correct answer is option 4.