MCQ practice · SSC Chemistry Board questions · Chapter 3: Structure of Matter
²³⁵₉₂U + ¹₀n → ᴬ₅₆X + ⁹²₃₆K + 3 ¹₀n + heat energy What is the value of A in this reaction?
Think it through first, then pick an option.
- a 140
- b 141
- c 142
- d 143
Answer and explanation
Correct answer: b 141
The mass numbers add up the same on both sides: 235 + 1 = A + 92 + 3, so A = 141.
Why the other options are wrong
- a 140: The left side is 235 + 1 = 236. The right side is A + 92 + 3, so A = 236 take away 92 and 3 = 141. A value of 140 counts four neutrons.
- c 142: 142 counts two neutrons instead of three. 236 minus 92 minus 3 gives 141.
- d 143: 143 counts only one neutron on the right, but there are three. 236 minus 92 minus 3 gives 141.
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