किसी बड़े हॉल में ध्वनि स्रोत को बंद करने के बाद भी बार-बार होने वाले परावर्तन के कारण ध्वनि का कुछ देर तक बना रहना क्या कहलाता है?

Taking a glass of water and freezing it by placing it inside a freezer is an example of which type of change and process?

Which of the following statements is/are true about air pressure? (A) Air around us exerts very less pressure on us. (B) Air contracts on heating and expands on cooling. (C) Warm air rises up and cooler air tends to sink towards the earth's surface. (D) As warm air rises, air pressure at that place is decreased.