It isn't possible to give a definitive ID just using online photos. Details of location of find are very useful e.g. grassland, under specific varieties of trees.
However that looks like a white gilled amanita species, quite possibly Amanita virosa known as Destroying Angel. As the name suggests it is deadly poisonous with no known antidote so wash your hands thoroughly after handling. Another less alarming option is possibly White Dapperling, Leucoagaricus leucothites which is non-poisonous.
Err on the side of caution and never pick up white gilled mushrooms.
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