I'm sure someone could correct me or provide more information if needed:
The answer is false: transmission loss doesn't decrease with the frequency of sound. The wording here could get you (I had to read it a few times) but the question looks like it is asking if the transmission loss decreases (with what I assume) when the frequency increases.
I do agree that it could've been more specific at the end with what changes the frequency of sound does (whether it increases or decreases).
But as the frequency of sound increases so does the transmission loss. A lower frequency consists of longer wavelengths which usually passes through most objects (imagine feeling/hearing the bass of a subwoofer from the next room over). The higher the frequency the shorter the wavelength which usually get blocked by a barrier. The mass or construction of the barrier also plays a part in determining the transmission loss. I've uploaded a few photos from an old source that shows this occurrence. And from MEEB (9th edition, chapters 27 & 28) talks about frequencies and transmission loss.
MEEB 9th Edition
Sound Proofing Company
Domestic Sound Proofing
MNE PSU EDU
custom audio direct
technic on acoustics