The correct answer is B. Graphite.
Graphite is a crystalline form of carbon that is naturally occurring. It is a good conductor of electricity and heat, and it is used in a variety of applications, including batteries, lubricants, and electrodes.
Diamond is a crystalline form of carbon that is also naturally occurring. However, it is not a good conductor of electricity. This is because the carbon atoms in diamond are arranged in a tetrahedral structure, which does not allow for the flow of electrons.
Iodine is a non-metallic element that is solid at room temperature. It is not a good conductor of electricity. This is because the iodine atoms are arranged in a molecular structure, which does not allow for the flow of electrons.
Sodium chloride is a salt that is commonly known as table salt. It is a crystalline solid that is composed of sodium and chlorine ions. Sodium chloride is not a good conductor of electricity in the solid state. This is because the sodium and chlorine ions are held together in a crystal lattice, which does not allow for the flow of electrons.
In conclusion, the substance which conducts current in the solid state is B. Graphite.