Given below is a table containing a few metals and non-metals with exceptional properties. Fill the spaces by identifying X, Y, and Z in the table.

$\begin{array}{cccc}\text{Sl.}& \text{Element}& \text{Category}& \text{Exceptional Property}\\ 1.& \text{Graphite (C)}& \text{Non-metal}& \text{Conducts electricity}\\ 2.& \text{Magnesium (Mg)}& \text{Non-metal}& \text{Hardest natural substance}\\ 3.& \text{Iodine (I)}& \text{Non-metal}& \text{Z}\\ 4.& \text{Potassium (K)}& \text{Y}& \text{Soft (can be cut with knife)}\\ 5.& \text{X}& \text{Metal}& \text{Low M.P. (melts in hand)}\end{array}$