Which of the following gases is commonly present under pressure in carbonated soft drinks to give them fizz and effervescence?

Introduction / Context:
Carbonated soft drinks are popular beverages recognised by their fizz and bubbles. This effervescence comes from a gas that is dissolved in the liquid under pressure during bottling or canning. When the container is opened, the pressure is released and the gas escapes as bubbles. The question asks which gas is typically used in soft drinks to produce this effect. Understanding this is a simple but important application of gas solubility and pressure in everyday life.

Given Data / Assumptions:

• We are dealing with ordinary carbonated soft drinks such as soda and cola.
• The drink is bottled under pressure.
• The options include nitrous oxide, oxygen, nitrogen, carbon dioxide and hydrogen.
• Basic knowledge of food and beverage technology is assumed.

Concept / Approach:
The gas most commonly used in soft drinks is carbon dioxide. Under high pressure, carbon dioxide dissolves in water to form carbonic acid, giving the drink its characteristic tangy taste. When pressure is released, CO2 escapes as bubbles. Nitrogen is sometimes used in specialty beverages like some stout beers to create a different type of foam, but typical soft drinks use carbon dioxide. Nitrous oxide is used in whipped cream dispensers, and hydrogen or oxygen are not used to carbonate beverages due to safety and taste issues.

Step-by-Step Solution:
Step 1: Recall that standard sodas and fizzy drinks are often labelled as carbonated beverages. Step 2: Carbonation refers to dissolution of carbon dioxide gas in water under pressure. Step 3: When a bottle or can is opened, the pressure drops, and carbon dioxide escapes, producing bubbles and fizz. Step 4: Nitrous oxide is associated with whipped cream and some food foams, not typical soft drink carbonation. Step 5: Therefore, the gas in question is carbon dioxide.

Verification / Alternative check:
Ingredient labels on soft drink bottles often state that the product contains carbonated water, meaning water with dissolved carbon dioxide. Food science references and industrial descriptions of soft drink production also refer to carbonation with CO2, not with nitrogen or oxygen. Some specialty drinks use nitrogen to create a creamy texture, but those are distinct from standard carbonated soft drinks, confirming CO2 as the usual gas.

Why Other Options Are Wrong:
Option A, nitrous oxide, is used as a propellant in cream chargers but not as the main gas in soda. Option B, oxygen, would promote oxidation and is not used because it can affect flavour and stability. Option C, nitrogen, is used in some beer and coffee products but is not the standard choice for soft drinks. Option E, hydrogen, is flammable and unsafe for beverage carbonation. Only option D, carbon dioxide, correctly identifies the gas responsible for the fizz in most soft drinks.

Common Pitfalls:
Some students may confuse nitrous oxide with carbon dioxide because both names end in oxide. Others may think nitrogen is used because air is mostly nitrogen. Remember that beverage labels explicitly mention carbonation and that CO2 has the right properties of solubility, taste contribution and relative safety for this purpose. Reading product labels is a simple way to remember the correct gas used in carbonated soft drinks.

Final Answer:
The gas present under pressure in soft drinks is Carbon dioxide, which dissolves in the drink and escapes as bubbles when the container is opened.