Correct Answer: $\frac{18}{23}$

Solution : Given:
$\frac{13}{17}$ : $\frac{17}{13}$ :: $\frac{23}{18}$ : ? :: $\frac{33}{26}$ : $\frac{26}{33}$

Like, $\frac{13}{17}$ : $\frac{17}{13}$→The given pair of fractions consists of two fractions. The first fraction has 13 as the numerator and 17 as the denominator. In the second fraction, the numerator and denominator are interchanged concerning the first fraction. Therefore, the second fraction has 17 as the numerator and 13 as the denominator.
And, $\frac{33}{26}$ : $\frac{26}{33}$→The given pair of fractions consists of two fractions. The first fraction has 33 as the numerator and 26 as the denominator. In the second fraction, the numerator and denominator are interchanged concerning the first fraction. Therefore, the second fraction has 26 as the numerator and 33 as the denominator.
Similarly, for $\frac{23}{18}$ : ?→The given pair of fractions consists of two fractions. The first fraction has 23 as the numerator and 18 as the denominator. In the second fraction, the numerator and denominator will be interchanged concerning the first fraction. Therefore, the second fraction will have 18 as the numerator and 23 as the denominator.

So, $\frac{18}{23}$ is related to $\frac{23}{18}$. Hence, the fourth option is correct.