Tea kept in a thermos flask is vigorously shaken. If the tea is considered as a system, then its temperature will

Answer: Option A

As thermos flask is insulated no heat energy added or taken from the system so, by first law of thermodynamics we can write $$dU=-\delta W$$   as we work done on the system is negative so, the internal energy will be positive. And therefore there will be a raise in temperature.