Which one of the following state- ment, is not correct ?

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Q: (CDS-II/2019)

Which one of the following state- ment, is not correct ?

question_subject: 

Science

question_exam: 

CDS-II

stats: 

0,28,36,13,28,16,7

keywords: 

{'elements': [0, 0, 2, 5], 'same atomic number': [0, 0, 0, 1], 'atoms': [0, 0, 0, 2], 'atom': [0, 0, 0, 2], 'nucleus': [1, 0, 1, 0], 'protons': [0, 0, 0, 1], 'different mass number': [0, 0, 0, 1], 'valency': [0, 0, 0, 1], 'nucleons': [0, 0, 0, 2], 'mass number': [0, 0, 0, 3], 'capacity': [1, 2, 4, 6], 'isobars': [3, 1, 4, 4], 'number': [0, 0, 0, 2]}

The correct answer is option 2. This statement is not correct because isobars are defined as atoms that have the same mass number but different atomic numbers. Isobars have different numbers of protons and electrons, which is why they have different atomic numbers. However, they have the same mass number because the mass number is equal to the sum of protons and neutrons in the nucleus.

Let`s look at the other options to understand them better. Option 1 is correct because elements are defined by the number of protons they possess. The number of protons determines the atomic number and the identity of an element.

Option 3 is also correct. The mass number of an atom is equal to the number of nucleons in its nucleus. Nucleons include both protons and neutrons. The mass number represents the total number of protons and neutrons in the nucleus.

Option 4 is also correct. Valency is the combining capacity of an atom. It indicates the number of electrons an atom can share, gain, or lose in order to form chemical bonds. Valency determines how an atom can interact with other atoms to form compounds.

In conclusion, only option 2 is not correct. Isobars have the same mass number but different atomic numbers