Answer: One neutron
Explanation:
one neutron 1/0n
Sum up the mass numbers on the right 99 + 135 + 2 = 236.
The sum of the mass numbers on the left should equal 236. 235 + 1 = 236
To solve this problem we will apply the concepts related to destructive interference from double-slit experiments. For this purpose we will define the path difference as,

Here,
= Wavelength
= Angle when occurs the interference point of destructive interference
Our values are given as,


Using the previous expression we have,





Therefore the distance between the two openings is 
Answer:
When Helium is identified by astronomers is one of the great triumphs of spectroscopy.
Explanation:
Janssen managed to do this great triumphs on August 18, 1868 . Janssen was the first person to introduce the helium, an element that never seen before on Earth, in the solar spectrum. At that time, he didn’t know that what he’d seen—he just think that it was something new. In the mid of 1800, the spectroscope instrument is introduced in astronomy.
Later on we heard that all helium in Universe has been created by the fusion of hydrogen nuclei.
To know more about Spectroscopy:
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The mathematical relationship between force and extension for a spring is F = -kx , where F is the restoring force, k is the spring constant and x is the extension. If a box that weighs 40 N is hung from a spring of content 400 N/m, then the extension is equal to x = -F / k = -400 / 40 = -10 cm. The negative sign simply shows the extension and restoring force are in opposite directions. The answer is 10 cm.