A coloured compound (A) reacts with dilute H_2SO_4 to produce a colourless gas (B) and colourless solution (C). The reaction between (B) and the acidified K_2Cr_2O_7 solution produces a green solution and a slightly yellowish precipitate (D). The substance (D) burns in air to produce a gas (E) which also can change colour of K_2Cr_2O

A coloured compound (A) reacts with dilute $$H_2SO_4$$ to produce a colourless gas (B) and colourless solution (C). The reaction between (B) and the acidified $$K_2Cr_2O_7$$ solution produces a green solution and a slightly yellowish precipitate (D). The substance (D) burns in air to produce a gas (E) which also can change colour of $$K_2Cr_2O_7$$ solution.

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