Asample of a substance has these characteristics:
• melting point or 9811 k
• hard. brittle solid at room temperature
• poor conductor of heat and electricity as a solid
• good conductor of electricity as a liquid or in an aqueous solution
this sample is classified as
(1) a metallic element
(2) a radioactive element
(3) a molecular compound
(4) an ionic compound

Those characteristic belong to an ionic compountd. Ionic compounds have strong bonds between their atoms (ionic bond is the strongest molecular bond) which conferes this kind of compounds high melting point, wich 9811 K is. Ionic compounds do not transmit current, because they do not have free electrons, like metals do, then they are poor conductors as solid. Ionic compounds dissolve in water into ions which are charges that can move, becoming then good conductors. The structure of ionic compound is a net of cristals which make them hard and brittle. Then, the answer i s option (4) an ionic compound.