When sealed biscuits are kept in the refrigerator for some time, they become crunchy because -

Concept:

Refrigerator:

• A refrigerator is a device that maintains a system or a body at a temperature lower than the surrounding temperature.
• In the refrigerator, the heat is removed from the low-temperature body and is rejected to the high-temperature body.
• Generally, the surrounding atmosphere acts as the high-temperature body for a refrigerator.​

Coefficient of Performance:

• The coefficient of performance is defined as the ratio of the desired output to the work input.
• The coefficient of performance of a refrigerator is given as,

\(⇒ COP_{R}=\frac{Q_{L}}{W}=\frac{Q_{L}}{Q_{H}-Q_{L}}=\frac{T_{L}}{T_{H}-T_{L}}\)

Where QL = heat removed from the system, QH = heat given to the surrounding, W = work input, TL = temperature of the system, and TH = temperature of the surrounding

Explanation:

• In many biscuits, under outside the high sugar content tends to absorb water from the atmosphere, ultimately resulting in a soft biscuit.
• Since it's cold & dry inside the refrigerator, you may keep biscuits/cookies, with wrapper intact.
• In a refrigerator, this process is obstructed due to very low temperatures. As a result, the biscuits do not soften.
• Those biscuits/cookies would remain crisp and taste good even after a month or two of opening the wrapper.
• However, when biscuits stored in a refrigerator are kept outside for some time, even they turn soft.

So the correct option will be, Humidity is low inside the fridge and hence excess moisture is absorbed.