Answer:
The concentration of this sodiumhydroxide solutions is 0.50 M
Explanation:
Step 1: Data given
Mass of sodium hydroxide (NaOh) = 8.0 grams
Molar mass of sodium hydroxide = 40.0 g/mol
Volume water = 400 mL  = 0.400 L
Step 2: Calculate moles NaOH
Moles NaOH = mass NaOH / molar mass NaOH
Moles NaOH = 8.0 grams / 40.0 g/mol
Moles NaOh = 0.20 moles
Step 3: Calculate concentration of the solution 
Concentration solution = moles NaOH / volume water
Concentration solution = 0.20 moles / 0.400 L
Concentration solution = 0.50 M
The concentration of this sodiumhydroxide solutions is 0.50 M
 
        
             
        
        
        
Answer:
for what school? It's different for all sadly :(
Explanation:
 
        
             
        
        
        
Answer: Option (D) is the correct answer.
Explanation:
Atomic number of chlorine is 17 and its electronic distribution is 2, 8, 7.  
So, in order to attain stability it tends to gain one electron from a donor atom. Therefore, a chlorine ion is formed as 
.
As it gains only one electron that is why, -1 charge occurs. 
Whereas Ar is a noble gas with atomic number 18. As it has completely filled octet so it will be unreactive in nature as it is already stable.
Similarly, He is also a noble gas so it is unreactive in nature.
Atomic number of boron (B) is 5 with electronic distribution 2, 3. So, in order to attain stability it needs to lose 3 electrons. 
Thus, we can conclude that Cl is the atom which tends to gain 1 valence electron from another atom in order to become stable.