The fomula is NH4 (1+)
There are only two elements N and H.
As per oxidation state rules, the most electronegative element will have a negative oxidation state and the other element will have a positive oxidation state.
N is more electronative than H, so H will have a positive oxidation state and nitrogen will have a negative oxidation state.
You can also use the rule that states the hydrogen mostly has 1+ oxidation state,except when it is bonded to metals.
In conclusion the oxidation state of H in NH4 (1+) is 1+.
Now you must know that the sum of the oxidations states equals the charge of the ion, which in this case is 1+.
That implies that 4* (1+)  + x =   1+
=> x = (1+) - 4(+) = 3-
Answer:  the oxidation state of N is 3-, that is the option b. 
        
             
        
        
        
To create the Lewis structure we need to take into account the octet rule: atoms tend to gain, lose or share electrons to complete their valence shell with 8 electrons.
C belongs to Group 4A in the periodic table so it has 4 valence electrons. It needs to share 4 pairs of electrons to complete the octet.
F belongs to Group 7A in the periodic table so it has 7 valence electrons. Each F needs to share 1 pair of electrons to complete the octet.
As a consequence, in CF₄, C will form a single bond with each F and all the octets will be complete.
 
        
             
        
        
        
As the earth is in the form of a sphere, the angle of incidence of the sun's rays at the earth's surface increases from the equator towards the poles and therefore the amount of heat received on a GIVEN AREA diminishes in the same direction. Temperature is therefore normally hottest near the equator and coolest near the poles. 
 
        
             
        
        
        
Answer:
A) IV: number of hours DV: score
Explanation:
Coz,
IV- is the variable that u change 
DV- is the variable that u test or measure
In this case, we need to change the hours of studying to see how studying for different hours [1 hr, 2hr, etc (( Independant variable coz we're changing the no. of hours)) ] is going to affect the student's score, and in the end, we are measuring the score of each student [this is the dependant variable].