The correct word to fill in the blank is "scorching." The sentence is expressing that whether it's chaat or a refreshing lemonade, lemon is essential during extremely hot summers. "Scorching" is used to describe intense heat, making it the appropriate choice in this context.

"Manifest" means to display, show, or reveal something clearly. The antonym "disguise" involves concealing or hiding one's true identity or the true nature of something. So, in a short explanation, while "manifest" involves revealing, "disguise" involves concealing or hiding.

"Impetuous" describes someone who acts suddenly without thought or care, often in a rash or impulsive manner. The antonym "calm" represents a state of tranquility and composed behavior, which is the opposite of being impetuous.

"Obsolete" refers to something that is no longer in use or outdated, while "contemporary" refers to something that is current or modern.