Substance A is mixed with water and donates 0.4% of its H⁺ ions, therefore given substance is a weak acid & show poor conduction of electric current.
According to the Arrhenius theory of acids and bases, acids are those species which gives H⁺ ion to the solution.
In the question it is given that, substance A is mixed with water and it donates H⁺ ion, from this it is clear that given substance is acid. It is also mention that it donates only 0.4% of its H⁺ ion means partial dissociation is observed, so we conclude that this acid is weak in nature. And due to weak dissociation and less number of available H⁺ ion it did not conduct electricity effectively.
Hence, option (D) is correct i.e. it is weak acid and a poor conductor of electric current.
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