Answer: After several days, a large bubble of gas collected in the upside-down beaker contains OXYGEN.
Explanation: 
Plants are known to be be autotrophic (producers) through the use of inorganic substance such as water, carbondioxide and light energy from sunlight in a process known as photosynthesis. 
An experiment was carried out by Latecia for investigation of the gas production of a water plant. It's therefore expected that OXYGEN gas which is the by-product given off during photosynthesis in green plants would be collected from the upside down beaker as gas bubbles.
 
        
             
        
        
        
the one that is considered a chemcial mutagen is : Tobacco Chemical mutagen refer to the substance that affected the DNA of those who consume the substancce or their offspring. Studies showed that consuming tobacco has proven to created DNA deformations for the fetus if it consumed by pregnant women.
 
        
             
        
        
        
<h2>Axons </h2>
Explanation:
Axons cross from one side of the spinal cord to the other through the gray commisure 
- Each arm or extension of the gray matter in the spinal cord is referred to as a horn
- Projecting towards the back of the spinal cord are the dorsal horns (or posterior horns)
- Projecting towards the front are the ventral horns (or anterior horns)
- In the thoracic and upper lumbar regions of the cord, an additional pair of side projections occur, which are called the lateral horns
- A narrow band of gray matter known as the gray commissure stretches across of the center of the spinal cord and connects the two sets of horns
- In the middle of the gray commissure is the central canal, which contains cerebral spinal fluid