In the following question, out of the four alternatives, choose the one which can be substituted for the given words/sentence. An instrument that is specifically used for measuring the pressure of gases in closed containers or systems.

Introduction / Context:
The question asks for the correct one-word substitute for the descriptive phrase "an instrument for measuring pressure of gases." Such questions test your knowledge of technical vocabulary, especially terms used in physics and engineering. Many different measuring devices exist, and they often sound similar, so it is important to know exactly which quantity each one measures.

Given Data / Assumptions:

• We need an instrument that measures the pressure of gases.
• The device is used for pressure, not temperature, speed, or length.
• The options given are barometer, anemometer, micrometer, manometer, and hygrometer.
• Only one option correctly fits the definition in a precise, scientific way.

Concept / Approach:
In basic science, different instruments measure different physical quantities. A barometer measures atmospheric pressure, an anemometer measures wind speed, a micrometer measures very small lengths or thicknesses, a hygrometer measures humidity, and a manometer is used for measuring the pressure of gases or liquids, especially in closed systems like pipelines or laboratory setups. The phrase in the question clearly focuses on gas pressure, which matches the function of a manometer most accurately.

Step-by-Step Solution:
Step 1: Identify the physical quantity in the definition: pressure of gases.Step 2: Recall that pressure is a force per unit area exerted by a gas or liquid on the walls of its container.Step 3: Match each option with its standard use. Barometer measures atmospheric pressure in the open air, anemometer measures wind speed, micrometer measures small dimensions, hygrometer measures moisture content in the air.Step 4: Note that a manometer is specifically designed to measure pressure of gases (and sometimes liquids) in a system, often relative to atmospheric pressure.Step 5: Conclude that manometer is the only option that exactly matches the given description.

Verification / Alternative check:
If the question had said "instrument for measuring atmospheric pressure" then barometer would be correct. However, the wording is broader and focuses on gas pressure in general, which is what manometers are commonly used for, including gas lines, laboratory experiments, and industrial systems. This confirms that manometer is the most precise choice for the description given in the exam question.

Why Other Options Are Wrong:
Barometer measures atmospheric pressure and is not normally used for pressure in closed gas systems. Anemometer measures wind speed, which is related to moving air rather than static pressure. Micrometer measures small distances or thicknesses, not pressure. Hygrometer measures humidity of air, not pressure. None of these fits the required definition as accurately as manometer.

Common Pitfalls:
Many learners confuse barometer and manometer because both involve pressure measurements. A helpful tip is that barometers are associated with weather and atmospheric pressure, while manometers are associated with gas pressure in pipes, tanks, and laboratory apparatus. Remembering this distinction will help avoid errors in similar questions.

Final Answer:
manometer