Answer A.
Which sentence below? INCORRECT about carbon-14?
A. It and nitrogen always exist in equal amounts in any substance.
B. Its half-life is more than 5,000 years.
C. It can decay to nitrogen-14.
D. It is radioactive.
Answers B, C, and D have the information found in the text.
B + C: – Citing the first sentence of paragraph 2: “Carbon- 14 has a half-life of 5, 570 years, which means that after that number of years, half of the carbon- 14 atoms have decayed into nitrogen-14 ”: Carbon-14 has a half-life of 5,570 years, which means that after every seven years, half of the carbon-14 atoms has decomposed to nitrogen-14.
D- Quote in the last sentence of paragraph 1: “Since a radioactive substance such as carbon-14 has a known half-life, […]”: Because a radioactive substance such as carbon-14 has a known half-life, […]) →Carbon-14 is a radioactive substance.
The remaining answer A is not correct.