The natural sources of oxalic acid, lactic acid and methanoic acid respectively are:

Table 2.3 of the NCERT chapter ("Some naturally occurring acids") lists the following pairs:

• Oxalic acid $\rightarrow$ Tomato
• Lactic acid $\rightarrow$ Sour milk (Curd)
• Methanoic acid $\rightarrow$ Ant sting (and also Nettle sting)

Matching the three acids named in the question (oxalic acid, lactic acid, methanoic acid) in that order gives exactly tomato, curd, ant-sting, which is option (A).

• (B) tomato, orange, nettle-sting — orange is the natural source of citric acid as per Table 2.3, not lactic acid, so this is wrong for the second acid.
• (C) orange, milk, ant-sting — orange gives citric acid, not oxalic acid; and while curd (sour milk) contains lactic acid, plain "milk" is not the source named in the chapter.
• (D) orange, sour milk, nettle-sting — again, orange is the source of citric acid, not oxalic acid, so the first pairing is incorrect even though the other two terms individually appear in Table 2.3.

Only option (A) correctly matches all three acids to their NCERT-listed natural sources.