The correct answer for this question is option 3, Issac Newton. He was the scientist who first used a glass prism to obtain the spectrum of sunlight.

Option 1, C. V. Raman, is not the correct answer because he is known for his work in the field of scattering of light, which led to the discovery of the Raman effect.

Option 2, Lord Rayleigh, is also not the correct answer. Lord Rayleigh, also known as John William Strutt, was a British physicist who made significant contributions to the study of sound, vibrations, and the scattering of light. However, he did not use a glass prism to obtain the spectrum of sunlight.

Option 4, S. Chandrasekhar, is not the correct answer either. Subrahmanyan Chandrasekhar was an Indian astrophysicist known for his groundbreaking work on the structure and evolution of stars. His work was not specifically related to obtaining the spectrum of sunlight using a glass prism.

Therefore, the correct answer is Issac Newton, who first used a glass prism to obtain the spectrum of sunlight.