Hydrogen has one electron in its outermost shell, while fluorine has seven electron in its outermost shell, hence both hydrogen and fluorine needs a single electron to complete its outermost shell. 
That's why there is a single bond between hydrogen and fluorine. 
Hence both hydrogen and fluorine share one electron with each other, so option "A" is correct.
        
             
        
        
        
The Doppler effect occurs when a source of sound or light 
moves either toward or away from the observer. 
        
             
        
        
        
Answer:
The awnser is d
Explanation:
i know cause i took the test
 
        
                    
             
        
        
        
Answer:
At light intensity I = 3, is P a maximum
Explanation:
Given:

now differentiating the above equation with respect to Intensity 'I' we get

or

or

or

Now for the maxima 
thus,

or

or

or

or
I = 3
thus, <u>for the value of intensity I = 3, the P is maximum</u>
at I = 3

or

or

 
        
             
        
        
        
Answer:
the third law (for every action there is an equal and opposite reaction).
Explanation:
The skateboarder pushes backwards on the road (that is he applies a force on the road in a direction opposite the direction of intended motion). By Newton's third law, this action of the skateboarder causes an equal reaction of the road on the skateboarder in the opposite direction. Newton's third law states that action and reaction are equal but opposite in direction. So, the road in response to this backward force pushes the skateboarder in the forward direction causing the skateboarder and the skateboard to move in the forward direction.