Question

Two isotopes of Uranium have 92 electrons each and have 144, 148 neutrons respectively.

Mass numbers of these two isotopes will be respectively

(A)237 ,236

(B) 236 ,237

(C) 236 ,238

(D)238 ,236​

Answer 1

Explanation:

(D)238 ,236

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Answer 2

The given options are incorrect. The mass numbers of the given isotopes will be 236 and 240 respectively.

• Mass number is the sum of protons and neutrons in an element.
• In this case, we are not provided directly with the number of protons but the number of protons in an element is equal to the number of electrons in it.
• Therefore the number of protons for each isotope will be 92.
• Their mass numbers will be:
• 92 + 144 = 236
• 92 + 148 = 240