Asample of a substance has these characteristics: melting point of 984 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

The correct answer is option 4, that is, an ionic compound.  

The mentioned features belong to an ionic compound. The ionic compounds exhibit strong bonds in between their atoms, that is, an ionic bond is the strongest molecular bond, this confirms that ionic compounds exhibit a high melting point.  

The ionic compounds do not transmit current, as they do not possess free electrons, like metals, thus, they are poor conductors as solid. The ionic compounds get dissolve in water and form ions that are the charges, which can move, making them good conductors as a liquid. The composition of the ionic compound is a set of crystals that makes them brittle and hard.