Is methy orange positive or negative??And how do we know that?

It is Positive. 

As per Quinonoid Theory of Indicators, each corrosive base pointer exists in two tautomeric frames, the benzenoid shape and the quinonoid shape. The two structures have diverse hues. The two structures change focuses with change in medium. Since, they have distinctive hues in various mediums, the medium is quite recently changing when shading is changing accordingly giving us an appropriate indicate be considered as the purpose of balance. 

For the methyl orange, the quinonoid frame is red in shading and is available overwhelmingly in acidic arrangement and the benzenoid shape is yellow in shading and is available transcendently in fundamental arrangement. The underneath balance is kept up by the two structures. Furthermore, these both contains Nitrogen and nitrogen is certain , thus Methyl orange is additionally positive.