948 or 9.48 x 10^2
There are two sets of rules for significant figures
•	One set for addition and subtraction
•	Another set for multiplication and division
You used the set for multiplication and division.
This problem involves addition and subtraction, and the rule is
The number of places after the decimal point in the answer must be <em>no greater than the number of decimal places in every term</em> in the sum.
Thus, we have
 78.9
 +890.43
 -21.
= 948.33
The "21" term has the fewest digits after the decimal point (none), so the answer must have no digits after the decimal point.
To the correct answer is 948 = 9.48 x 10^2. It has three significant figures.
 
        
             
        
        
        
STP is abbreviation for Standard Temperature and Pressure at which the temperature is 273 K and pressure is 1 atm 
- At these conditions the molar volume is equal to 22.4 L
so 1 mole of SO₂ volume = 22.4 L 
     ? mole of SO₂ volume = 2.5 L
number of moles = 2.5 / 22.4 = 0.1116 mol
mass of SO₂ = 0.1116 * 64.063 = 7.15 g
        
                    
             
        
        
        
Answer:
They will create an ionic bond.
Explanation:
The atom with the one valence electron will lose its one, because it's a metal and metals will lose electrons to become stable. The nonmetal (with 7 valence electrons) will gain that electron, therefore creating a stable octet for the nonmetal, making the compound stable.
 
        
             
        
        
        
Answer:
The further an electron is from the nucleus. the greater its energy level.
Explanation:
When an electron is close to the nucleus, it is at as low an energy level as it can get.
We must put energy into an electron to pull it away from the attraction of a nucleus.
So, electrons that are further from the nucleus are at higher energy levels.