Option 4 is correct, i.e. Theory of photoelectric effect.
Albert Einstein:
He was born at Ulm, in Württemberg, Germany, on March 14, 1879.
Prize motivation: "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect".
Albert Einstein won Nobel Prize in Physics in 1921.
Albert Einstein is a German-born physicist who also developed the special and general theories of relativity.
Photoelectric effect - A phenomenon in which electrically charged particles are released from or within a material when it absorbs electromagnetic radiation. The effect is often defined as the ejection of electrons from a metal plate when light falls on it.