Answer: Invalid
Explanation:
The conclusion should be [tex]p \to r[/tex] due to the hypothetical syllogism rule (similar to the transitive rule).
You can make a truth table to show that the premises [tex]p \to q[/tex] and [tex]q \to r[/tex] can both be true at the same time, but the conclusion [tex]p \leftrightarrow q[/tex] is false. Whenever you have all true premises and a false conclusion, then the argument is invalid. True premises must lead to a true conclusion.
