Have a control. You have to have something to compare your experimental results or else your results could be random chance.
Answer:
Xe
Explanation:
Cs and Na are solids in room temperature while F and Xe are gases.
The number of electrons in the outermost shell of an atom will determine its reactivity. Out of the gases given Xe and F, F ( the most electronegative element) posses 5 valence shell electrons which makes it highly reactive while Xe which is a noble gas posses 8 valence shell electrons which makes it less reactive compared to many elements.
Given that,
The speed of a wave, v = 200 m/s
Wavelength, 
We need to find the frequency of this wave. The relation between wavelength, frequency and the speed is given by :
So, the frequency of this wave is 100 Hz.
Answer:
They can preserve food in the cans, in the refrigerator and make them frozen, in the green houses to preserve them in the off season.
This is all how you can preserve food in the off season.
<h3>Hope this helps.</h3><h3>Good luck ✅.</h3>
