Solder help please please please?

Common tin/lead solder forms a eutectic solution and the melting temperature (and crystallization) depend upon the proportion of tin to lead. The solder (alloy) will melt at a lower temperature than either the tin or lead alone making it more convenient to work with. the bond strength depends upon the proportion of lead to tin but the joint will remain strong at temperatures well below the melting point. Lead free solder is now used for water supply plumbing because of the toxicity of lead.