If a potato is placed on a pure paper plate which is white and unprinted and put in a microwave oven, the potato heats up but the paper plate does not. This is because:

Microwaves heat materials primarily by dielectric heating: the alternating electromagnetic field forces polar molecules (notably water) to oscillate, producing thermal energy. The efficiency of microwave heating therefore depends strongly on moisture-dependent dielectric properties; materials with high free water content absorb and convert microwave energy into heat much more effectively than dry materials [1]. A potato contains substantial water (and starch as a carrier of that water), so it heats rapidly in a microwave, whereas a plain white paper plate is largely cellulose with very little free water and a low dielectric loss factor, so it does not appreciably heat under the same conditions [1]. Thus option 3 is correct.

Sources

1. [1] https://eprints.nottingham.ac.uk/43232/2/New%20Insights%20into%20RF%20and%20Microwave%20drying%20of%20foods.pdf
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 30: Climatic Regions > Potatoes > p. 459