Explanation:

Isobars are atoms (nuclides) of different chemical elements that have the same number of nucleons. Correspondingly, isobars differ in atomic number (or number of protons) but have the same mass number. In Geography, Isobars are lines on a weather map joining together places of equal atmospheric pressure . On the map the isobar marked 1004 represents an area of high pressure, while the isobar marked 976 represents an area of low pressure. Hence option 4th is correct.