It's a secret, sorry.
The most common letter for a last name for people in the United States is "S".
Susan
The S&P500 Index ETF, ticker SPY.
The name goes back to the Middle Ages, although not common. The name became most common in the 1900's
The most common animal/s are insects.The most common insect is a fly
The name of the Union;s aerial spy balloon was the Intrepid. The balloon was in the Union;s service but owned by its "pilot" Thaddeus Lowe. The intention was to spy on Confederate positions at the Battle of Seven Pines. Too much wind delayed the flight and then the forests prevented getting a clear view of the battlefield.
carbonate
I don't think it's ever been common, but it was more common in the 30's-40's.
Owen Wilson
probably Jacob or Joshua. i know a LOT of Jacob s... so yeah.James and John are the most common first names for boys.
The most common brakes on a tractor trailer are the s-cam brakes
The most common ion formed by sulfur is the sulfide ion (S2-).