Situation dependent. The squad may be broken down to replace lost members of other squads, or another squad may be broken down to replace lost members of that and other squads. Reservists may be called up as replacements, new inprocessing soldiers may be sent as replacements, etc.
Platoon sergeant
platoon leader, platoon sergeant, and squad leader
The weapons squad squad leader who is the most seasoned E-6 in the platoon, that is until a new E-7 and LT are put in the platoon
None. The chain of command goes directly from squad level to platoon level.
The squad of troops joined the platoon, therefore they are contingent with the platoon.
a Squad.
Fire team, squad, platoon, or A-team
A squad is just 1 rank of a platoon. Usually they have mixed mos's but all are trained for infantry.
In military terminology, a squad is a sub-subunit led by a non-commissioned officer that is subordinate to an infantry platoon.
Fire team, squad, platoon, or A-team
Typically it would be the rifleman in 3rd Squad Bravo Team.
Squad Leaders "fall in" first, and in order of first second third, facing the Platoon Sergeant with one arm's distance between them front to back. The respective squad's members fall in to the left of the Squad Leaders, generally in Fire Team order (1st 2nd 3rd). The Platoon Sergeant centers him/herself on the formation and when giving commands faces the formation. The Platoon Commander centers him/herself just behind and facing the back of the formation. Here's a diagram: Squad Leaders < < < < < < < < < < < < < < < PLT SGT > < < < < PLT Cmnder < < < < < < < < < < < < < < <