Because the pizza is hot then ice cream so the smell of pizza is easily spread by the process of diffusion
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Pizza is generally served hot. The particles of the hot pizza , being heated have high kinetic energy which easily overcome the intermolecular force of attraction and diffuses into the air which we get as a mouth watering smell . But in case of cold ice cream the particles are much more cold than that of the hot particles of the pizza. Hence they have low kinetic energy which do not allow the particles to overcome the high intermolecular force of attraction and get diffused in the air thus finally reaching our nose.
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