Which solution below would turn litmus paper red?
a) ba(oh)2
b) naoh
c) nh3
d) hc2h3o2

Litmus paper turns red in acidic conditions whether its blue or red litmus ,its not NH3 (ammonia)  , neither is it barium hydroxide (A)  , sodium hydroxide (B) will make it blue or remain blue (depemding on type of paper used ) so it has to be D which is the chemjcal formula for acetic acid , hope this helps ! 

Cr(oh)3 -> cr(3+) + 3oh-