Final answer:
The pair with the first member being more covalent than the second is SnF4, CF4 because carbon has a smaller size and higher electronegativity than tin, leading to a greater sharing of electrons and increased covalent character in CF4.
Step-by-step explanation:
The pair of compounds where the first member should be more covalent than the second member is SnF4, CF4. This is because as we move from tin (Sn) to carbon (C) in the periodic table, the electronegativity difference between the central atom and fluorine decreases, leading to more sharing of electrons (covalent character) rather than electron transfer (ionic character). In SnF4, the larger size and lower electronegativity of Sn compared to C in CF4 means Sn-F bonds have more ionic character relative to the C-F bonds in CF4 which are more covalent.