The correct answer is option 4: 1, 2, and 3. Let`s break down each statement to understand why it is correct or incorrect.

Statement 1: Plutonium-239 can be made artificially. This statement is correct. Plutonium-239 is not found naturally and is instead produced by bombarding Uranium-238 with neutrons.

Statement 2: Boron is used in a nuclear reactor to absorb unwanted neutrons. This statement is also correct. Boron is commonly used as a control rod material in nuclear reactors to absorb the excess neutrons and regulate the rate of fission.

Statement 3: In nature, the availability of Uranium-238 is much more than that of Uranium-235. This statement is correct as well. Uranium-238 is the most abundant isotope of uranium, comprising 99.3% of natural uranium, while Uranium-235 is relatively rare, making up only 0.7% of natural uranium.

Therefore, all three statements are correct, and the correct answer is option 4: 1, 2, and 3.