The refractive indices of ice, kerosene, benzene, and rock salt are different. Which option correctly lists these materials from left to right in increasing order of refractive index?

Introduction / Context:
Refractive index is a measure of how much the speed of light is reduced in a medium compared with its speed in vacuum. Different materials have different refractive indices, and knowing the relative values helps in understanding refraction, lens design, and optical instruments. This question asks you to identify the correct increasing order of refractive index for four common materials: ice, kerosene, benzene, and rock salt.

Given Data / Assumptions:
- Materials mentioned are ice, kerosene, benzene, and rock salt.- The correct order should have the smallest refractive index first and the largest last.- Approximate standard refractive indices from textbooks are assumed.

Concept / Approach:
Refractive index n of a material is defined as n = c / v, where c is the speed of light in vacuum and v is the speed of light in the medium. Higher refractive index means light travels more slowly and bends more when entering the material from air. Standard approximate values used in school level physics are: ice around 1.31, kerosene around 1.44, benzene around 1.50, and rock salt around 1.54. To find the increasing order, you sort these from the smallest value of n to the largest.

Step-by-Step Solution:
1. Note the approximate refractive index of ice: n(ice) is about 1.31.2. Note the approximate refractive index of kerosene: n(kerosene) is about 1.44.3. Note the approximate refractive index of benzene: n(benzene) is about 1.50.4. Note the approximate refractive index of rock salt: n(rock salt) is about 1.54.5. Arrange these values from the smallest to the largest: 1.31 (ice) < 1.44 (kerosene) < 1.50 (benzene) < 1.54 (rock salt).6. Translate this ordered list into the corresponding option: ice, kerosene, benzene, rock salt.

Verification / Alternative check:
You can cross check this ordering by remembering some general trends. Water and ice typically have refractive indices slightly above 1.3. Many organic liquids like kerosene and benzene have higher values in the 1.4 to 1.5 range, and crystalline salts often show even higher refractive indices. This broad trend supports the detailed ordering obtained from the approximate numerical values. Textbook tables of refractive indices also list these materials in similar ranges, confirming the correct sequence.

Why Other Options Are Wrong:
- Rock salt, benzene, kerosene, ice: This reverses the order completely and places the highest index first and the lowest last.- Rock salt, ice, benzene, kerosene: This mixes the order and incorrectly places rock salt before ice.- Kerosene, ice, benzene, rock salt: This places kerosene before ice and disturbs the correct ascending order.

Common Pitfalls:
Students sometimes try to guess based only on whether a substance is solid or liquid, which can be misleading. Another error is to assume that density and refractive index always follow the same pattern, which is not strictly true. The safest approach is to memorise common refractive indices for key materials or at least remember that ice has a lower index than kerosene, kerosene is lower than benzene, and benzene is lower than rock salt. This memory aid will help you quickly identify the correct order in exams.

Final Answer:
The increasing order of refractive index is ice, kerosene, benzene, rock salt.