Question: What timer is supported for broadcast but not for groupcast?
Option 1: SL HARQ RTT timer
Option 2: SL inactivity-timer
Option 3: SL on-duration timer
Option 4: SL HARQ retransmission timers
Explanation: According to the text, only SL on-duration timer is supported for broadcast. This implies that while SL on-duration timer is used for both groupcast and broadcast, it is the only one of these timers specifically mentioned as being supported for broadcast.