When suspended in water, each ball will experience an upthrust exerted by the surrounding water. By N3L, each ball will exert an equal but opposite downward force on the surrounding water (“downthrust”).
Since silver is less dense than lead, a 1-kg silver ball has a larger volume than a 1-kg lead ball.
This means that the silver ball will displace more water than the lead ball. The silver ball will experience a larger upthrust, which implies it also exerts a larger downward force on the water.
The balance will tip downward on the silver ball side.
(Btw, if both balls are not suspended, but rested fully on the bottom of the beaker, the balance will remain balanced.)