The melting point of element X is 686 degree C. X is a good conductor of electricity in it's solid & molten states. Deduce the bonding &...

Because this element is a good conductor of electricity,
and has a high melting point it is quite likely a metal.  Non-metals tend to be poor
conductors of electricity, and have lower melting points than
metals.

Now that we know that this element is a metal we
know that the bonds it will form will be ionic (bond between a metal and a non-metal). 
In ionic bonding electrons are transferred rather than shared.  The transferring of
electrons causes an electrostatic attraction between the two elements causing them to
come to gather.

Also because the bond is ionic we know that
the bond it forms will likely be crystalline.