A certain compound (X) when treated with copper sulphate solution yields a brown precipitate. On adding hypo solution the precipitate turns white. The compound is

KI reacts with CuSO4​ solution to produce cuprous iodide (white precipitate) and I2​ (which gives brown colour). Iodine reacts with hypo solution. Decolourisaiton of solution shows the appearance of white precipitate.CuSO4​+2KI→CuI2​+K2​SO4​2CuI2​→White ppt.2CuI​+BrownI2​​  I2​+2Na2​S2​O3​→colourlessNa2​S4​O6​​+2NaI