A nucleic acid was analyzed and found to contain 32% adenine, 18% guanine, 17% cytosine and 33% thymine. The nucleic acid must be -

According to Chargaff's rules, in any sample of double-stranded DNA The amount of adenine equals the amount of thymine The amount of guanine equals the amount of cytosine. The total amount of purines (i.e. adenine and guanine) equals the total amount of pyrimidines (i.e. cytosine & thymine) In the given question purines (adenine 32% & guanine 18%) are equal to pyrimidines (thymine 33% & cytosine 17%). Adenine (32%) is equal to thymine (33%) and guanine (18%) is equal to cytosine (17%). Thus it is double-stranded DNA.