UPSC NDA I 2021 General Ability Solved Paper

Concept:Solder is a fusible metal alloy used to join metal pieces. Common soft solder is an alloy of lead ($\text{Pb}$) and tin ($\text{Sn}$).Explanation:Soldering uses a filler metal (solder) that melts below the melting point of the workpieces.The most widely used soft solder consists of tin ($\text{Sn}$) and lead ($\text{Pb}$).Tin belongs to Group 14 of the periodic table (atomic number 50, atomic mass 118.710 amu).Lead also belongs to Group 14 (atomic number 82, atomic mass 207.2 amu).This $\text{Pb}$-$\text{Sn}$ alloy has a low melting point and good wetting properties.Another type, hard solder, is an alloy of copper ($\text{Cu}$) and zinc ($\text{Zn}$), but it is not the common solder referred to in basic questions.Thus, solder is primarily an alloy of lead and tin.Answer:C. Pb and Sn.