The usual composition of a soldering alloy is

The correct option is "Tin and lead".

The usual composition of a soldering alloy is a mixture of tin (Sn) and lead (Pb) in varying proportions, commonly 60% tin and 40% lead or 63% tin and 37% lead (known as eutectic solder).

Tin provides good wettability, which helps the solder spread smoothly over the metal surfaces.

Lead lowers the melting point of the alloy and provides strength and durability to the soldered joint.

This combination creates an alloy with a relatively low melting point, making it ideal for soldering applications in electronics and electrical work.

Why not the others?

"Tin, lead and small percentage of antimony" is used in bearing alloys, not in common solder.

"Tin, lead and silver" forms a type of hard solder, used where stronger joints are required, but it is not the usual composition.

"Tin and copper" is used in lead-free solders (modern alternatives), but traditionally the common solder is tin-lead.

Therefore, the usual composition of a soldering alloy is tin and lead.