At ordinary conditions near room temperature, which of the following substances has the maximum density among the options given?

Introduction / Context:
Density is defined as mass per unit volume and is a key physical property used to compare substances, predict floating or sinking behaviour, and design processes in chemistry and physics. Many exam questions test your understanding of relative densities of common substances such as water, ice, organic liquids, and gases. This question asks which of the listed substances has the maximum density under ordinary conditions, highlighting the unusual behaviour of water compared to its solid form and to other organic compounds.

Given Data / Assumptions:

• The substances listed are water, ice, ethylene, and acetone.
• Water is liquid water near room temperature (or at its maximum density around 4 degrees Celsius).
• Ice is the solid form of water.
• Ethylene is a gas at room temperature.
• Acetone is an organic liquid commonly used as a solvent.
• We assume standard atmospheric pressure and typical laboratory conditions.

Concept / Approach:
Most substances become denser when they freeze, but water is anomalous: ice is less dense than liquid water, which is why ice floats. At around 4 degrees Celsius, water attains its maximum density, close to 1 g/cm^3. Common organic liquids such as acetone typically have densities lower than water, making them lighter and causing them to float or mix differently. Ethylene is a gas at room temperature and therefore has a very low density compared to liquids and solids. Among the given options, liquid water is therefore denser than ice, acetone, and gaseous ethylene under ordinary conditions.

Step-by-Step Solution:
Step 1: Compare water and ice. Ice floats on water, which means ice is less dense than liquid water; thus, water has higher density than ice. Step 2: Consider ethylene. Ethylene is a gas; gases generally have much lower densities than liquids and solids at the same temperature and pressure. Step 3: Consider acetone. Acetone is a volatile organic liquid with a density lower than that of water, so equal volumes of acetone weigh less than water. Step 4: Conclude that water, which is a dense liquid, has the maximum density among the options.

Verification / Alternative check:
Approximate numerical values support this conclusion. Liquid water at 4 degrees Celsius has a density close to 1 g/cm^3. Ice has a density around 0.9 g/cm^3, which is why it floats. Acetone has a density of less than 1 g/cm^3, often quoted around 0.79 g/cm^3, making it lighter than water. Ethylene, as a gas, has a density of only a few grams per litre, making it orders of magnitude less dense than any of the liquids or solids listed. These values confirm that water has the greatest density among water, ice, ethylene, and acetone under standard conditions.

Why Other Options Are Wrong:
Option B (Ice): Ice is less dense than water, which is why icebergs and ice cubes float on the liquid surface. Option C (Ethylene): Being a gas, ethylene has very low density compared to liquids and solids. Option D (Acetone): As a typical organic solvent, acetone is less dense than water and would not have the maximum density among the listed substances.

Common Pitfalls:
A common misconception is that solids are always denser than their corresponding liquids. While this is true for many substances, water is a famous exception due to hydrogen bonding and its open crystal structure in ice. Students may also focus on the word “ice” and assume it must be heavier without recalling that ice floats on water. Another error is ignoring the gaseous nature of ethylene and making a random guess. Remember that the anomaly of water (liquid denser than solid) is a favourite exam concept and helps you quickly identify water as having the maximum density among these options.

Final Answer:
Among the given substances, Water has the maximum density under ordinary conditions.