What type of chemical bond holds nacl an ionic crystal together

Ab c or d ? i’m not sure what the answer is

What is the correct name for the compound cocl3? a) cobalt(i) chloride b) cobalt(i) chlorate c) cobalt(ii) chlorate d) cobalt(iii) chloride

Which statement is true about the model of the electromagnetic spectrum a: it change the frequencies of light. b: it compare wavelengths of light. c: the color of light waves can be changed using the model. d: the intensities of light waves can be decreased using the model.