Two nuclides are isotones if they have the same number of neutrons but have a different number of protons.  Identify four isotone symbols for ²³³Pa

• A. ²³²Ac, ²³²Th, ²³²Cm, ²³²Bk
• B. ²³¹Ac, ²³²Th, ²³⁴U, ²³⁵Np
• C. ²³¹Pa, ²³²Pa, ²³⁴Pa, ²³⁵Pa
• D. ²²⁹Ac, ²³⁰Th, ²³¹Cm, ²³³Bk

Answer: (B)