Answer:
D. Burning paper
Explanation:
physical change is just changing the way it looks
chemical change is changing the properties of the object or thing
melting ice is just changing the way it looks it still has the same atoms and elements.
when you burn something it will change the properties of the atoms in the object
 
        
             
        
        
        
Answer:

Explanation:
Here by ideal gas equation we can say

now we know that pressure is kept constant here
so we will have

since we know that number of moles and pressure is constant here
so we have

now we know that initial temperature is 17.8 degree C
and finally volume is doubled
So we have

so final temperature will be


 
        
             
        
        
        
Answer: addition of electrons and hydrogen ions. loss of electrons and addition of hydrogen ions. loss of electrons and either addition or loss of hydrogen ions.
 
        
             
        
        
        
  Answer: The answer is 1.5 hours.
Step-by-step explanation: Given that the pilot took 1/2 hour to complete 1/3rd of his trip. We are to calculate the time that he will take to complete his trip.
Time taken by the pilot to complete 1/3 rd of his trip = 1/2
Therefore, time taken by the pilot to complete his trip is given by

Thus, the pilot will take 1.5 hours to complete his trip. 
 
        
             
        
        
        
A wave is a disturbance that propagates, or moves from the place it was created. The simplest waves repeat themselves for several cycles and are associated with simple harmonic motion. Let us start by considering the simplified water wave in Figure 2. The wave is an up and down disturbance of the water surface. It causes a sea gull to move up and down in simple harmonic motion as the wave crests and troughs (peaks and valleys) pass under the bird. The time for one complete up and down motion is the wave’s period T. The wave’s frequency is 
f
=
1
T
f
=
1
T
, as usual. The wave itself moves to the right in Figure 2. This movement of the wave is actually the disturbance moving to the right, not the water itself (or the bird would move to the right). We define wave velocity vw to be the speed at which the disturbance moves. Wave velocity is sometimes also called the propagation velocity or propagation speed, because the disturbance propagates from one location to another.