Compare the given fractions and replace '$\boxed{\phantom{653}}$' by an appropriate sign '< or >':

(i) $\dfrac{3}{6} \boxed{\phantom{653}} \dfrac{5}{6}$

(ii) $\dfrac{2}{7} \boxed{\phantom{653}} \dfrac{2}{5}$

(iii) $\dfrac{3}{5} \boxed{\phantom{653}} \dfrac{4}{5}$

(iv) $\dfrac{4}{7} \boxed{\phantom{653}} \dfrac{4}{9}$

(i) $\dfrac{3}{6}$ and $\dfrac{5}{6}$

These are like fractions (same denominator 6).

In like fractions, the fraction with greater numerator is greater.

Since 3 < 5, therefore, $\dfrac{3}{6} \lt \dfrac{5}{6}$.

Hence, $\dfrac{3}{6} \lt \dfrac{5}{6}$.

(ii) $\dfrac{2}{7}$ and $\dfrac{2}{5}$

These are unlike fractions with same numerator 2.

In fractions with same numerator, the fraction with smaller denominator is greater.

Since 7 > 5, therefore, $\dfrac{2}{7} \lt \dfrac{2}{5}$.

Hence, $\dfrac{2}{7} \lt \dfrac{2}{5}$.

(iii) $\dfrac{3}{5}$ and $\dfrac{4}{5}$

These are like fractions (same denominator 5).

In like fractions, the fraction with greater numerator is greater.

Since 3 < 4, therefore, $\dfrac{3}{5} \lt \dfrac{4}{5}$.

Hence, $\dfrac{3}{5} \lt \dfrac{4}{5}$.

(iv) $\dfrac{4}{7}$ and $\dfrac{4}{9}$

These are unlike fractions with same numerator 4.

In fractions with same numerator, the fraction with smaller denominator is greater.

Since 7 < 9, therefore, $\dfrac{4}{7} \gt \dfrac{4}{9}$.

Hence, $\dfrac{4}{7} \gt \dfrac{4}{9}$.