In a periodic square wave, how to change in a particular condition?
If $T_1$ remains constant and $T\rightarrow\infty$ then you get a single square pulse of length $2T_1$. There won't be another square pulse because the period is infinite.

$T_1$ constant and $T\rightarrow 0$ is indeed nonsensical because the definition of the signal assumes $T_1 &lt; T/2$.

If $T$ is constant, you can get a constant function if $T_1=T/2$ (and not $2/T$).

If $T$ is constant and $T_1\rightarrow 0$ your function becomes 0. You will only get an impulse if you keep the area under the rectangle constant, i.e. if its height increases as its width decreases.