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countable and uncountable, plural heliums
(uncountable) The second lightest chemical element (symbol He) with an atomic number of 2 and atomic weight of 4.002602, a colorless, odorless and inert noble gas. quotations examples
It was an enormous balloon filled with helium, that elemental gas forged from hydrogen in the nuclear furnace of the stars.
1997, Ian McEwan, Enduring Love, Vintage (1998), page 3
(countable) A form or sample of the element. examples