Identify the electron configuration of Zr.  

• A. 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s¹4d³
• B. 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶4d⁵
• C. 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d²
• D. 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶4d⁴

Answer: (C)