GMAT Sentence Correction (SC) | Re: In order to ensure that chemical reaction in the lab behave

Please go through this post:https://www.manhattanprep.com/gmat/forums/rather-than-accept-the-conventional-wisdom-that-the-earth-t1177.html
It explains that RAHER THAN is a conjunction and hence can be followed by anything but INSTEAD OF is a complex preposition which should be followed by a noun. The noun can be a gerund as well.

With this, use of INSTEAD OF could be correct if we had the sentence as:

it is important the heat be applied evenly over
...

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