Aluminium has the fewest valence electrons available for bonding. 
As we go across the groups from left to right, we have the following numbers of valence electron. 
• Group 13: Al = 3 
• Group 14: C = 4 
• Group 15: N = 5 
• Group 17: Cl = 7 
Thus, Al has the fewest valence electrons available for bonding.