This lovely Haydn theme was written in 2/4 time. There are 2 beats to the measure and a quarter note gets one count.
The song begins softly and the "surprise" is a suddenly very loud chord, the G chord on the second beat in measure 16.
To hear this theme played by an orchestra go to Essentials of Music Click on "Composers"
Haydn, Franz Joseph (1732-1809)
Symphony No. 94 in G major "Surprise"
Listen to the second selection on the page.