Mass number = protons + neutrons
mass number = 5 + 7
mass number = 12
Combination
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Answer:
A chemical equation consists of the chemical formulas of the reactants (on the left) and the products (on the right). The two are separated by an arrow symbol (“→” usually read aloud as “yields”). ... The equation also identifies that all the compounds are in the gaseous state.
Explanation:
D. The number increases and then decreases for noble gases