Answer:
C
Explanation:
Elements in the same group (in this case, group 1 or group 1a) have similar chemical properties. The only one in the same group as Sodium (group 1) is Cesium.
A) Neon (Group 8a)(Group 18)
B) Magnesium (Group 2a)(Group 2)
C) Cesium (Group 1a)(Group 1)
D) Phosphorous (Group 5a)(Group 15)
