What is the entropy for an irreversible adiabatic process?

[eprparadox]

Homework Statement

The change in entropy is zero for:
A. reversible adiabatic processes
B. reversible isothermal processes
C. reversible processes during which no work is done
D. reversible isobaric processes
E. all adiabatic processes

Homework Equations

$dS = \frac{dQ}{T}$

The Attempt at a Solution

The answer here is A.

But intuitively, I don't understand why it is that the entropy is zero only for a reversible adiabatic process.

What is it about irreversible processes that make the entropy increase? Is it that we can't have irreversiable processes that are adiabatic? Any examples to provide that can help me with intuition here?

 

[Chestermiller]

Here is a Physics Forums Insights article on how to determine the entropy change for an irreversible process (including adiabatic irreversible processes): https://www.physicsforums.com/insights/grandpa-chets-entropy-recipe/