If two soap bubbles of unequal radii are connected by a tube,

The excess pressure inside a soap bubble of radius $R$ is given by $P = \dfrac{4T}{R}$, where $T$ is the surface tension.

For a smaller bubble, the radius $R$ is less, so the excess pressure $P$ is greater.

When two bubbles of unequal radii are connected by a tube, air flows from the region of higher pressure to the region of lower pressure.

Therefore, air flows from the smaller bubble to the larger bubble. As air flows out of the smaller bubble, its radius decreases further, increasing the pressure even more, while the larger bubble grows.