Which of the following refers to the change in wavelength that occurs when an object moves toward or away from a source?
a) doppler effect
b) chromatic aberration
c) spectroscopy
d) wave theory of light

A) Doppler effect

Explanation:

As we know that when Sound source travel with respect to observer then due to relative motion of source and observer the frequency of sound emitted by the source is observed slightly different by the observer.

This change in the frequency of the sound observed by the observer is known as Doppler's Effect

So here we know by the formula of doppler's effect the frequency is given as

so here since the frequency observed is different from real frequency so the wavelength observed by the observer is changed

so correct answer will be

A) Doppler effect

it is given that trillions of microbes make up to 1% to 3% of the body mass.

let's take average of this percentage: 2%

consider the average mass of the human body as 70 kg.

then, trillions of microbes would have mass  

therefore, 100 trillion micro-organisms would weigh:

this is an approximate value and could change depending on the mass of the human body and percentage of the microbes present in it.

average mass per microorganism =