Answer:
"h" signifies Planck's constant
Explanation:
In the equation energy E = h X v
The "h" there signifies Planck's constant
Planck's constant is a value, that shows the rate at which the energy of a photon increases/decreases, as the frequency of its electromagnetic wave changes.
It was named after Max Planck who discovered this unique relationship between the energy of a light wave and its frequency.
Planck's constant, "h" is usually expressed in Joules second
Planck's constant = 
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Helium has an atomic mass of 4.00 atomic mass units.
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