Which of the following statements is not true about glucose?

Glucose is present in pyranose form, i.e., five-membered ring structure. Thus, option (iii) is correct because the given statement is incorrect.

Glucose is a monosaccharide that is composed of six carbon atoms with an aldehyde group. Thus, it is an aldohexose. So, this statement is true and therefore, option (i) is incorrect.

Option (ii) is incorrect because the given statement is true. On heating glucose with HI, it forms n-hexane. This reaction suggests that all the six carbon atoms in glucose are linked in a straight chain.

Option (iv) is incorrect because the given statement is true. The aldehyde group is not free in the cyclic structure. So, it does not give 2, 4-DNP test.