Why do the two methylene protons in ethylbenzene have a chemical shift at 2-2.9?
Protons attached to a carbon that is connected to a benzene ring typically resonate in the range 2.2-2.9 ppm (see the Ar-CH range in this table).

Here is the proton nmr spectrum for ethylbenzene.  The methylene protons absorb around 2.7 ppm, right in the upper end of the expected range.

 

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