Two of the stable isotopes of mercury are 198hg and 202hg. these isotopes emit slightly different wavelengths of light, 546.07532nm and 546.07355nm, respectively. to identify which isotopes are included in a sample of mercury, we can shine the light it emits on a diffraction grating with a screen 4 m away. how many lines per centimeter are necessary in the diffraction grating for the first-order bright fringes of the two wavelengths to be 1.6 cm apart on the screen?