Explanation: The full form of GPS is Global Positioning System. It is a satellite-based navigation system that provides accurate information about the location, speed, and time anywhere on Earth. Developed by the U.S. Department of Defense, GPS uses a network of at least 24 satellites orbiting the Earth. It is widely used in navigation, mapping, military operations, aviation, and smartphone tracking applications.

Argon (Ar) is an inert gas, also known as a noble gas. It belongs to Group 18 of the periodic table, whose elements are characterized by complete outer electron shells, making them chemically unreactive. Argon constitutes about 0.93% of the Earth's atmosphere and is widely used in electric bulbs, welding, and in creating inert environments for chemical reactions.

Other options (for context)

• Hydrogen: Highly reactive and combustible gas.
• Nitrogen: Relatively less reactive but not inert; forms compounds like ammonia.
• Oxygen: Highly reactive gas essential for combustion and respiration.

Explanation: Chikungunya is a viral disease caused by the Chikungunya virus, which belongs to the Togaviridae family. It is transmitted to humans through the bite of infected Aedes aegypti and Aedes albopictus mosquitoes. The disease causes sudden fever, joint pain, headache, and rash. In contrast, cholera (caused by Vibrio cholerae), typhoid (by Salmonella typhi), and tuberculosis (by Mycobacterium tuberculosis) are all bacterial diseases.

Explanation: When a car moves forward while rain is falling vertically, the rain appears to fall at an angle relative to the car’s motion. As a result, the raindrops strike the front windscreen of the car, not the rear screen. This is due to the relative velocity between the car and the falling rain.

Explanation: Sodium hydroxide (NaOH) is a base, so it does not turn blue litmus paper red. Instead, it turns red litmus paper blue. In contrast, lemon juice, acetic acid, and hydrochloric acid are acidic and turn blue litmus red.

Explanation: A concave lens always forms a virtual, erect, and diminished image, regardless of the position of the object. The image formed appears on the same side of the lens as the object and is used in devices like spectacles for correcting short-sightedness (myopia).

Explanation: Acids do not turn red litmus to blue; instead, they turn blue litmus paper red. Acids are sour in taste, corrosive in nature, and have a pH value less than 7. Therefore, the statement that acids turn red litmus to blue is incorrect.

Explanation: The primary colours of light are Red, Green, and Blue (RGB). These are the fundamental colours that can be combined in different proportions to produce all other colours in the visible spectrum. Yellow is not a primary colour—it is a secondary colour formed by mixing red and green light. This principle of colour mixing is used in television, computer screens, and other digital displays that use RGB colour models.

The Moon takes about 27.3 days to complete one revolution around the Earth with respect to the stars (called the sidereal month). However, due to the simultaneous movement of the Earth around the Sun, the Moon takes approximately 29.5 days to complete one full cycle of phases (from new moon to new moon), known as the synodic month. This period is commonly rounded to 28 days in general usage.

Other options (for context)

• 45 days: Much longer than the Moon’s actual orbital period.
• 50 days: Incorrect — the Moon completes more than one revolution in this time.
• 65 days: Far too long compared to the real lunar cycle.