Answer:
Groups like the Halogens, which include Chlorine and Flourine, share similar properties both behaviorally and structurally. The Periodic Table is essentially a bunch of patterns and trends and the groups (like the one with Sodium and Potassium) were grouped together because of these similarities.
Explanation:
https://en.wikipedia.org/wiki/Alkali_metal
<u>Answer:</u> The wavelength of spectral line is 656 nm
<u>Explanation:</u>
To calculate the wavelength of light, we use Rydberg's Equation:

Where,
= Wavelength of radiation
= Rydberg's Constant = 
= Final energy level = 2
= Initial energy level = 3
Putting the values in above equation, we get:

Converting this into nanometers, we use the conversion factor:

So, 
Hence, the wavelength of spectral line is 656 nm
5 electrons
Boron atomic number 5 has five electrons in its ground state.
Commonly Boron will lose 3 electrons leaving 2 electrons in its most common ionic form.
Explanation:
The atomic number gives the number of protons. Protons which have a positive charge are balanced by an equal number of electrons in a neutral atom.
Boron number 5 has five protons and therefore as a neutral atom also has five electrons.
Boron has an electron configuration of
1s22s22p1
The most stable electron configuration for Boron is
1s2
+ 3 charges. By losing three electrons Boron can achieve the stable electron structure of Helium
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