8.3 grams HCl (1 mole HCl/36.458 grams)

= 0.23 moles HCl

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This is how you write HCl (Hydrochloric acid) in water:

HCl (aqueous) or short form HCl(aq)

The chemical formula (not symbol) of hydrogen chloride is HCl; for a diluted solution you can use "HCl dil." but this isn't a standard formula.

1 m HCl is not more reactive than 4m HCl, but 4m HCl is more concentrated.

Pure HCl is 36.5 mwt so 0.5M would be 18.25 g pure HCl. In practice HCl is not pure but supplied at 36.5 % HCl typically.