R.K.
Your son is not acting out. He is 16 months old. It is normal for him to drop or throw food from the high chair. The dropping is a way for him to learn about time and space.
The hitting, at his age he doesn't understand that when he touches you ---- you feel it too. Hitting is quite often a matter of muscle control. He is still a baby and needs to learn how to act and interact with people.
When he throws food take his plate away and sharply say NO to him. Give him back his plate and tell him to eat. He also needs to understand that eating is a scocial event. You should be sitting with him and eating dinner, too. If you place a plate of food in front of him and then walk away to do something else while he is busy and confined, he is missing a big part of the mealtime experience.
When he hits take his hand gently and again sharply say NO. Show him how to touch gently.
He will get it. He simply needs to learn.