Correct Option
Solder is a fusible metal alloy primarily used to join metallic workpieces through a process called soldering. In electronics, the most commonly employed solder is an alloy of lead (Pb) and tin (Sn). A typical composition, such as 60% tin and 40% lead, offers a relatively low melting point (generally between 180°C and 250°C), good electrical conductivity, and strong mechanical bonding, making it ideal for connecting delicate electronic components without causing thermal damage.
Incorrect Options
Iron and tin (A): Iron possesses a high melting point (1538°C) and poor fusibility, rendering it unsuitable for low-temperature soldering applications in electronics. While tin is a component of common solder, iron is not.
Aluminium and lead (C): Aluminium is generally not used in standard solder alloys because it readily forms a tenacious, passive oxide layer on its surface, which makes it difficult to wet and bond effectively with solder. Lead is a common component, but aluminium is not suitable.
Aluminium and iron (D): Both aluminium and iron have high melting points and exhibit characteristics (like oxide formation for aluminium and poor fusibility for iron) that make them unsuitable for use as primary components in solders for electronic applications, which require low melting temperatures and good wetting properties.