In a pack of cards, there are 52 cards. There are 4 suits: diamonds, hearts, spades and clubs.

To determine the probability of selecting a Queen from a standard deck of 52 cards, we can use the formula provided:

\[
P(A) = \frac{\text{Frequency in which Event A occurs}}{\text{Total number of observations}}
\]

In a standard deck of cards, there are 4 Queens (one from each suit: diamonds, hearts, spades, and clubs).

So:

- Frequency of selecting a Queen = 4 (there are 4 Queens in the deck)
- Total number of observations = 52 (the total number of cards in the deck)

Now, we can plug in these values into the formula:

\[
P(\text{Queen}) = \frac{4}{52}
\]

This can be simplified:

\[
P(\text{Queen}) = \frac{1}{13}
\]

From the options you provided (2/52, 4/52, 12/52), the correct answer is:

\(\frac{4}{52}\).