Chemistry
Assertion (A): The sum of the number of protons and neutrons present in the nucleus of an atom of an element is called its mass number.
Reason (R): The number of protons in the nucleus of an atom of an element is called its atomic number.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Atomic Structure
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Answer
Both A and R are true but R is not the correct explanation of A.
Explanation
Assertion (A) is correct because
Mass number = number of protons + number of neutrons in the nucleus.Reason (R) is also correct because
Atomic number = number of protons in the nucleus.
However, knowing what atomic number is does not explain what mass number is. Mass number depends on both protons and neutrons, while the Reason only talks about protons.
So both statements are true, but R does not correctly explain A.
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Reason (R): The number of protons and the number of electrons are equal in an atom.
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Reason (R): These circular orbits are associated with a fixed amount of energy.
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Fill in the blanks:
(a) Dalton said that …………… could not be divided.
(b) The fundamental particle of an atom carrying a negative charge is called …………… .
(c) An ion which has a positive charge is called a …………… .
(d) The outermost shell of an atom is known as …………… .
(e) The …………… of an atom is very hard and dense.
(f) Neutrons are …………… particles having mass equal to that of protons.
(g) Isotopes are the atoms of …………… element having the …………… atomic number but …………… mass number.