Answer:
Led is a light-emitting diode, a semiconductor diode that glows when a voltage is applied. So, there is always a sure result of whether a substance conducts electricity or not as the light glows. That is why it is a better option for testing conduction of electricity.
Explanation:
 
        
             
        
        
        
Answer:
2
3
Explanation:
To infer the last energy of the given atoms, we need to write their electronic configuration: 
For N = 1S² 2S² 2P³
      Mg  = 1S² 2S² 2P⁶ 3S²   
The energy levels are usually designated as;
    n = 1
    n = 2 
    n = 3 
    n =4 
For N, the last energy level is 2
      Mg, the last energy level is 3
We can also determine this number by the periods the atoms can be found. 
 
        
             
        
        
        
This is what i have found i hope this helps 
 
        
             
        
        
        
The elements in the periodice table are not listed in alphabetical order, because the arragement in rows (periods) and columns (groups or familes), in increasing order of atomic number (number of protons of the atoms) permits to explain similarities among the elements, trend in some properties, and even predict properties of unknown elements.
For example, the elements of the first group (family), called alkaline metals, all have 1 valence electron, have similar physical properties (ductibility, malleability, luster, thermal and electricity conductivity), react in similar way with water, show a trend in the atomic radii and in the ionization energy.
You can tell similar stories for other groups like, alkalyne earth metals, halogens and noble gases.
You can also tell trends in electroneativities, and atomic radii, for a row of elements, as per the order they are in the row.
So, the current array resulted very helpul for chemists to explain and predict the behavior and properties of the elements.