Chapter 4

NCERT
Class 9
Science
Solutions
2. Helium atom has an atomic mass of 4u and two protons in its nucleus. How many neutrons does it have?

Question:

Helium atom has an atomic mass of 4u and two protons in its nucleus. How many neutrons does it have?

Answer:

Mass number = Atomic mass = 4

Mass number = p + n

4 = 2 + n

n = 4 – 2

n = 2

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