A student measures the length of a pencil as 7.50 cm. The number of significant figures is MCQ with Answer and Explanation

Explanation:
Gamma rays >10¹⁹ Hz, highest.

Explanation:
At 0°C, speed ~ 331 m/s. At room temperature (20°C) ~ 343 m/s, often taken as 340. Increases with temperature v ∝ √T. For many problems 340 is used, but at 0°C it's 331. So option A.

Explanation:
Michael Faraday discovered electromagnetic induction (1831): changing magnetic flux induces EMF. Oersted found current-magnetism link; Ampere studied forces; Volta invented battery. Memory aid: 'Faraday = induction; Lenz = induced current direction'. History-based question testing key discoveries, frequently appearing in competitive exams.