Unit impulse vs Kronecker delta vs Dirac delta?
Kronecker Delta used mainly in context of discrete time signals is defined as $$\delta_{ij} $$ is 1 only when $i=j$ or $i-j=0$, $0$ otherwise. So alternatively it is also written as $\delta[i-j]$. This value is exactly 1 and finite (refer below for the distinction with Dirac Delta)

The unit impulse is just the kronecker Delta with $j=0$ hence we only refer to unit impulse with one parameter $\delta_i$. Since $j=0$, this is alternatively written as $\delta[i ]$.Hence is 1 at $i=0$, $0$ otherwise.

The continuous time unit impulse can be thought of derivative of continuous time unit step (modified to have a slightly less steep than the sudden step at $t=0$). Refer to Oppenheim's book on signals and systems Chapter 1.

The Dirac Delta is used in context of continuous time signals to define impulses. It is defined as having an infinitely small width and hence a large magnitude, however the area under the curve integrates to 1. Refer to Oppenheim's book on signal and systems for various shapes that a Dirac Delta function could take, in all cases the area being 1.