NEET UG CHEMISTRY MCQ: ORGANIC CHEMISTRY-SOME BASIC PRINCIPLES AND TECHNIQUES

Solution approach

1. Correct Answer + Core Reason: $\mathrm{CHClO}$. The empirical formula is determined by the mole ratio of C, H, Cl, and O.
   
   Step-by-Step Solution:
   
   Step 1: Convert percentages to moles by dividing by atomic masses:
   - Moles of C = $\frac{{18.5}}{{12}} = 1.54$
   - Moles of H = $\frac{{1.55}}{{1}} = 1.55$
   - Moles of Cl = $\frac{{55.04}}{{35.5}} = 1.55$
   - Moles of O = $\frac{{24.81}}{{16}} = 1.55$
   
   Step 2: Find the simplest whole number ratio by dividing by the smallest value (approximately 1.54 or 1.55):
   - C: $\frac{{1.54}}{{1.54}} = 1$
   - H: $\frac{{1.55}}{{1.54}} = 1$
   - Cl: $\frac{{1.55}}{{1.54}} = 1$
   - O: $\frac{{1.55}}{{1.54}} = 1$
   
   Step 3: Write the empirical formula:
   - Empirical formula = $\mathrm{CHClO}$
   
   Why other options are wrong:
   - Option A: $\mathrm{C}{\mathrm{H}_2}\mathrm{OCl}$: This formula would imply a different C:H:Cl:O ratio than the one calculated.
   - Option B: $\mathrm{C}{\mathrm{H}_2}\mathrm{Cl}{\mathrm{O}_2}$: This formula would imply a different C:H:Cl:O ratio than the one calculated.
   - Option C: $\mathrm{ClC}{\mathrm{H}_2}\mathrm{O}$: This formula would imply a different C:H:Cl:O ratio than the one calculated.
   
   Key Concepts:
   - Empirical Formula
   - Percentage Composition
   - Atomic Mass
   
   Memory Aids:
   - Remember to convert percentages to moles by dividing by atomic mass before finding the simplest ratio.
   
   Quick Tips:
   - Always divide by the smallest mole value to find the simplest whole number ratio.