50% probability that a human sperm cell will carry an X chromosome
 
        
             
        
        
        
Answer:
D. ususally very abundant in an ecosystem
Explanation:
Most commercial phosphorus is produced by mining and heating calcium phosphate. Phosphorus is the eleventh most abundant element in the Earth's crust
 
        
             
        
        
        
Im pretty sure that its nondisjunction
        
                    
             
        
        
        
Answer:
1. an eclipse of the Sun
2. state (phase) of matter
3. 5.0 g/cm3
Explanation:
1. Eclipse of the sun occurs when the planetary bodies align in such a way that causes the moon to block sunlight from reaching the Earth. The eclipse of the Sun will be the most predictable occurrence because it follows a pattern of occurrence. Eclipse of the sun occurs after a specific period of time, hence, based on this, scientists can predict that when it will occur next using its previous pattern of occurrence. 
2. Considering the following groups: Group A: water, aluminum, water vapor
Group B: gasoline, ice, air
Group C: alcohol, iron, oxygen
One would realize that each constituent of each group exists in a particular state of matter. For example, in group B, gasoline is a liquid, ice is a solid while air is a gaseous mixture. Same applies for group A and C where water and alcohol are liquids, iron and aluminum are solids, while water vapor and oxygen are gases. 
This shows that the STATE (PHASE) OF MATTER was the basis of classification. 
3. 
 
        
             
        
        
        
Answer:
The mechanism that Darwin proposed for evolution is natural selection. Because resources are limited in nature, organisms with heritable traits that favor survival and reproduction will tend to leave more offspring than their peers, causing the traits to increase in frequency over generations.
The reason that natural selection is important is that it's the central idea, stemming from Charles Darwin and Alfred Russel Wallace, that explains design in nature. It is the one process that is responsible for the evolution of adaptations of organisms to their environment.
Explanation:
hope this helps