Q1: Brittleness of cold is due to an excess of

ANS:C - phosphorus

Normally the steel has brittle by carbon content but,

To make steel brittle the steel is heated until that looks like red then sudden cool by water.

When the steel contains an excess of phosphorus content that brittle at low heat (is called COLD short steel).

When the steel contains an excess of sulphur content that brittle at high heat (is called HOT short steel).