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As per the question the wavelength of the microwave is given as 3.52 mm.
we are asked to calculate the frequency of the wave.
we know that microwave is a electromagnetic wave.
As per Clark Maxwell's electromagnetic theory ,every electromagnetic wave moves with a velocity equal to the velocity of light in vacuum and that is equal to 3×10^8 m/s.
From the equation of the wave,we know that velocity of wave is the product of frequency and wavelength.
Mathematically wave velocity
where f is the frequency of the wave and
is the wavelength.
As per the question 

Here 
Hence frequency of the wave 


Here Hertz [Hz] is the unit of frequency.
D. it is thickest in the middle
Answer:
Increase,.faster
Explanation:
The kinetic energy of the molecules inside the balloon
increases
which means they are moving
faster
I hope this helps you :)