Some data on the properties of Group I elements is given below. The table lists lithium, sodium, potassium and rubidium, together with melting point / ^{\circ}C and density in $\text{g cm}^{-3}$. Potassium has melting point $X$. Rubidium has melting point $Y$ and density $Z$. What values should $X$, $Y$ and $Z$ take?
- A$X = 63,\ Y = 252,\ Z = 0.26$
- B$X = 63,\ Y = 39,\ Z = 0.26$
- C$X = 39,\ Y = 63,\ Z = 1.53$
- D$X = 63,\ Y = 39,\ Z = 1.53$