When it come to boosting moves which boosts more, the plates or the other ones?

Question

Say if I want to give my Pokemon [say Glaceon] an item that boosts Ice type moves, which would boost the power of an Ice type move [say Ice Beam] more, NeverMelt Ice or Icicle Plate?

Answer 1

It doesn't matter. They both boost ice moves by 20%.

Hope this helps!

Answer 2

They both would boost Ice Beam by 20%.

Before Gen IV, Type-enhancing items would only boost 10%, but since Plates debuted in Gen IV, this does not matter.
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Source:

Bulbapedia/Type-enhancing item
Bulbapedia/Plates