Oxidation numbers is the right answer
Boron trichloride has a simple molecular structure,
whereas sodium chloride has a giant ionic lattice
structure. The ionic bonding between oppositely
charged ions in NaCl is stronger than the covalent
intramolecular bonding in BCl3. Therefore, less energy
is required to break the intramolecular covalent bonds in
BCl3, hence a lower melting temperature.
Ans: B) semiconductor
Photovoltaic cells work by converting light energy to electrical energy. These cells are essentially made of silicon based semiconductors. When photons (light energy) strike the surface of the semiconducting material electrons are let loose. The delocalization of electron creates a flow of charge which produces electricity.
Thus, it is the semiconductor present in a photovoltaic cell which is responsible for converting light to electricity.