Idiophones are instruments that produce sound with the vibration from their body. Castanets are non-pitched instruments and idiophones that are generally used in Spanish Folk Music.

You buy castanets from a supplier of musical instruments.

While this question makes no grammatical sense whatsoever, yes, castanets are percussive instruments.

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i would say acoustic guitar and trumpet

Yes, Lucero Tena plays the castanets. In Spanish, "castañuelas". Check her out on YouTube. She plays the castanets for flamenco as well as classical music. She is fantastic!