Explanation: Nitrogen makes up about 78% of Earth's atmosphere by volume, making it the most abundant gas in the air. Oxygen is the second most abundant gas, comprising about 21% of the atmosphere. Hydrogen and methane are present in much smaller concentrations.

Explanation: Internet is a global network of interconnected computers and servers that communicate using standard protocols. In contrast, Linux, Unix, and Windows are operating systems or families of operating systems.

Explanation: Measuring atmospheric pressure: This is the primary use of a barometer. Determining altitudes: A barometer can be used to estimate altitude based on changes in atmospheric pressure, as pressure decreases with increasing altitude. Weather forecasting: Changes in atmospheric pressure measured by a barometer can be used to predict weather patterns. A barometer is not typically used for measuring the density of liquids, so option 3 does not apply.

Explanation: Acids turn blue litmus paper red. The other properties listed are correct: A: All acids have a sour taste (e.g., citric acid in lemons). B: Many acids are corrosive in nature (e.g., sulfuric acid, hydrochloric acid). C: Acidic solutions have a pH less than 7.

Explanation: Radar systems use radio waves to detect and track objects such as aircraft. The radio waves are transmitted and then reflected off the object back to the radar system, which processes the returned signal to determine the object's location and movement.

Explanation: Bromine is the only non-metal that is a liquid at room temperature (approximately 20°C or 68°F). The other elements listed are either solids or gases at room temperature: Phosphorus: Solid Chlorine: Gas Helium: Gas