Which of the following was to be discovered first in the chromospheres of the sun?

Answer: Option D

The chromosphere (literally, "sphere of colour') is the second of the three main layers in the Sun's atmosphere and is roughly 2,000 kilometers deep. It sits just above the photosphere and just below the solar transition region. Helium, the lighter of the noble gases, was the first to be discovered. In fact, this element was first identified in the Sun's chromosphere rather than in the Earth.