Step 1: Recall the USP proof spirit relation.
Under the USP system, 100 degree proof spirit is defined as spirit containing 57.1% alcohol by volume. Any other alcohol strength is converted to a percentage of this proof strength using:
\[ \%\ \text{Proof Spirit} = \frac{\%\ v/v\ \text{alcohol} \times 100}{57.1} \]
Step 2: Substitute the given alcohol strength.
The elixir contains \( 47\% \) v/v alcohol, so:
\[ \%\ \text{Proof Spirit} = \frac{47 \times 100}{57.1} \]
Step 3: Calculate the value.
\[ \%\ \text{Proof Spirit} = \frac{4700}{57.1} \approx 82.3\% \]
This rounds to 82%, which is the closest listed option.
Step 4: Final Answer.
\[ \boxed{82\%} \]