What irq would com 2 normally use

IRQ 3.

The A+ tests are moronic when it comes to these questions. If they ask you IRQ for a network card the answer should be 5. LPT1 should be 7. The reason this is moronic is because all the A+ literature I've read also puts the sound card IRQ at 5. A+ makes it seem like IRQ 5 is the only free IRQ after setting up a PC.

You should commit these IRQs to memory only for passing the test. Unless you are working in pure DOS, there is no need to know them anymore.
IRQ 0: System Timer
IRQ 1: Keyboard controller
IRQ 2: Video card? (cascades with IRQ 9)
IRQ 3: Com2 or 4
IRQ 4: Com1 or 3
IRQ 5: Free (or LPT2)
IRQ 6: Floppy controller
IRQ 7: LPT1
IRQ 8: Real Time Clock
IRQ 9 (cascades with IRQ 2)
IRQ 10: Free
IRQ 11: Free
IRQ 12: PS/2 mouse
IRQ 13: Math co-processor
IRQ 14: Primary IDE
IRQ 15: Secondary IDE

Please note that this is from memory, so I may be a tad wrong.