The emf of cell 

It could be increased by :

A

decreasing concentration of both $$Tl^+$$ and $$Cu^{2+}$$ ions

B

increasing concentration of $$Cu^{2+}$$ ions

C

increasing concentration of $$Tl^+$$ ions

D

increasing concentration of both $$Tl^+$$ and $$Cu^{2+}$$ ions