UPSC CDS 2 2021 GK Paper

Concept:Solder is an alloy primarily composed of lead and tin, used for joining electrical components due to its low melting point.Explanation:Solder is a fusible metal alloy that typically contains $60\%$ tin and $40\%$ lead.It has a low melting point (around $600^\circ\mathrm{F}$) and good electrical conductivity.These properties make it ideal for welding electrical wires and connecting components on circuit boards.Among the given options, only $\mathrm{Pb}$ (lead) and $\mathrm{Sn}$ (tin) form solder.Other pairs like $\mathrm{Pb}$ and $\mathrm{Zn}$ (zinc), $\mathrm{Pb}$ and $\mathrm{Si}$ (silicon), or $\mathrm{Pb}$ and $\mathrm{Co}$ (cobalt) are not standard solder alloys.Answer:Option B: $\mathrm{Pb}$ and $\mathrm{Sn}$.