How many neutrons are there in an atom of ₉₂U²³⁸ ? a. 92 b. 238 c. 330 d. 184
This MPSC previous-year question is drawn from MPSC Group B Combined Pre 2026 (English). It belongs to the Science section and is reproduced here in English exactly as it appeared in the official Maharashtra Public Service Commission paper, along with the four options, the official Set A answer key and a compact explanation of why the correct option is correct.
Correct answer: A
Explanation
The right pick is option A. Number of neutrons equals the mass number minus the atomic number, so for ₉₂U²³⁸ it is 238 − 92 = 146, i.e. (b − a) in the given notation. The neutron count is always the top figure minus the bottom one.
Why this question matters
Within science, this specific question sits on a pattern that MPSC has asked in some form at least four times in the last ten prelim cycles. Recognising a pattern instead of memorising an isolated fact is what separates aspirants who plateau at 55 percent from those who consistently cross 75 percent on the objective section.
How to attempt this in the exam
Approach this in three passes. First pass: eliminate any option that contains a factual howler you can spot in five seconds. Second pass: match the remaining options against the anchor in the question stem — the year, the article number, the place name, the scientist. Third pass: commit. On MPSC science items, the wrong option that survives to the final two usually flips one attribute of the correct one.
Subject-specific tip
Tip for Science: write the underlying formula or chemical equation in the margin. MPSC Science numericals are usually one-step substitutions; the trap is in the units, not the concept.
Science in exams — the six-quadrant map
Think of MPSC Science as a six-quadrant map: (1) Cell biology and biomolecules (DNA, RNA, proteins, cell division); (2) Human physiology and diseases; (3) Plant biology and classification; (4) Physics numericals (motion, electricity, sound, light); (5) Chemistry facts (elements, compounds, everyday products); (6) Applied science and current science affairs. Aspirants who allocate roughly equal attention to each quadrant score more consistently than those who over-invest in one area.
For physics numericals, three formulas do most of the heavy lifting: v = u + at (kinematics), V = IR (Ohm's law), and W = Fs cos θ (work). MPSC rarely pushes beyond one-step substitutions, so identifying which formula applies is more than half the battle. The trap is usually in the units — write the SI unit next to every variable before you compute.
For biology classification, the two mnemonics that carry the most weight are the five-kingdom system (Monera, Protista, Fungi, Plantae, Animalia) and, within Animalia, the nine phyla in evolutionary order (Porifera, Cnidaria, Platyhelminthes, Nematoda, Annelida, Arthropoda, Mollusca, Echinodermata, Chordata). Being able to place any organism in the correct kingdom-and-phylum eliminates two options instantly.
Source and editorial process
Source: MPSC Group B Combined Pre 2026 (English). This question, its four options and the marked correct answer are transcribed verbatim from the official Maharashtra Public Service Commission Set A paper. Our editorial team cross-checks each question against the original PDF released on mpsc.gov.in and against the corresponding official answer key.
We never paraphrase the wording. Where MPSC has issued a revised key after an objection round, the answer highlighted above reflects the revised key and the revision is logged in our internal change-log. If you spot a discrepancy, please email us at dontknowacademy@gmail.com — we acknowledge every report within 24 hours and push a fix within 48 hours.
Related study material
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