Marie mixed 5g of carbon with 5g of lead oxide. she heated the mixture strongly for 15 minutes in a fume cupboard.

The problem talks about two questions and these are:

1.Metals are very good conductors of electricity and heat. Directing heat is easier. So let Marie heat the beads and also have heat another substance, for instance, water. If the beads heat quicker, then they are metals. Another test to conduct is called flame test. This test should give you a colored flame (blue/white for lead) the metal is lead if the reaction is: 2PbO+C ==> 2Pb +CO2

2.The beads are possibly to be lead since Ferrous(lead) oxide + carbon = carbon dioxide + lead 

You need to divided twenty four by a dozen them by the temperature it is getting cook by

Rn in the right answer