The correct answer is A. the magnet to become stronger 
The stronger the electric current in the piece of metal, the stronger the magnetic field will be.
        
                    
             
        
        
        
25/1500 is equal to 0.8/x
0.8*1500 is equal to 1200
1200/25 is equal to 48 N
        
                    
             
        
        
        
Explanation:
We have,
Semimajor axis is 
It is required to find the orbital period of a dwarf planet. Let T is time period. The relation between the time period and the semi major axis is given by Kepler's third law. Its mathematical form is given by :

G is universal gravitational constant
M is solar mass
Plugging all the values,

Since,
 
So, the orbital period of a dwarf planet is 138.52 years. 
 
        
             
        
        
        
D. A solution because it dissolves when mixed with water
        
                    
             
        
        
        
To solve this problem we will apply the expression of charge per unit of time in a capacitor with a given resistance. Mathematically said expression is given as

Here,
q = Charge
t = Time
R = Resistance
C = Capacitance 
When the charge reach its half value it has passed 10ms, then the equation is,




We know that RC is equal to the time constant, then

Therefore the time constant for the process is about 14ms