Final answer:
The correct order for turning off a suction apparatus is vacuum first, then the Buchner funnel, and finally the water aspirator.
Step-by-step explanation:
When turning off a suction apparatus like the one used in combination with a Buchner funnel, the correct order is important to avoid backflow and potential damage to the system. Firstly, you should turn off the vacuum source, which stops the suction process. Following this, you close the Buchner funnel to secure the filtration set-up and ensure no further air is pulled through. Lastly, the water aspirator, if used as the vacuum source, should be turned off to stop the flow of water. Hence, the correct order should be vacuum, Buchner funnel, water aspirator, which corresponds to option (b).