An earthquake is a catastrophic<span> event that results from a gradual accumulation of stresses at fault lines. Clearly </span>catastrophism<span> is at work.</span>
        
             
        
        
        
Answer:
An exothermic reaction releases energy. Endothermic takes in energy.
Explanation:
 
        
                    
             
        
        
        
Well I'm sure many a time you've seen on some science experiment someone wrap a copper wire around a nail well thats generally the idea for electromagnets you get a solid piece of iron which is the only metal that is magnetic and you wrap a copper wire around it and the idea is to make two opposing magnetic poles by aligning the molecules with a electrical charge (a battery) so now with all three pieces assembles you have a copper wire attached to two sides of a battery and wrapped around a nail
        
                    
             
        
        
        
Tin metal reacts with hydrogen fluoride to produce tin(II) fluoride and hydrogen gas according to the following balanced equation.
Sn(s)+2HF(g)→SnF2(s)+H2(g)
Sn(s)+2HF(g)→
SnF
2
(s)+
H
2
(g) 
How many moles of hydrogen fluoride are required to react completely with 75.0 g of tin?
Step 1: List the known quantities and plan the problem.
Known
given: 75.0 g Sn
molar mass of Sn = 118.69 g/mol
1 mol Sn = 2 mol HF (mole ratio)
Unknown
mol HF
Use the molar mass of Sn to convert the grams of Sn to moles. Then use the mole ratio to convert from mol Sn to mol HF. This will be done in a single two-step calculation.
g Sn → mol Sn → mol HF
Step 2: Solve.
75.0 g Sn×1 mol Sn118.69 g Sn×2 mol HF1 mol Sn=1.26 mol HF
75.0 g Sn×
1
 mol Sn
118.69
 g Sn
×
2
 mol HF
1
 mol Sn
=1.26 mol HF 
Step 3: Think about your result.
The mass of tin is less than one mole, but the 1:2 ratio means that more than one mole of HF is required for the reaction. The answer has three significant figures because the given mass has three significant figures.
        
                    
             
        
        
        
Answer:
higher energy level s...........