Answers
1.	8 electrons
2.	10 electrons
3.	10 electrons
4.	8 from the oxygen atom and 1 from each of the 2 hydrogen atoms
5.	4 hydrogen bonds
Explanation
The atomic number of oxygen is 8 thus it has a total of 8 electrons. When writing the electron configuration for the oxygen, the first n shell requires two electrons to complete the 1st orbital. The fact that 1s holds a maximum of 2 electrons the next 2 electrons of oxygen goes to 2s orbital. The 2s orbital takes a maximum of two electrons and the remaining 4 electrons occupy the 2p orbital. The configuration formed will be 1s² 2s² 2p4 .The maximum number of electrons in the second shell is 2n²=2×2² =8 from the formula 2n² (the maximum number of electrons in a shell). The total number of electrons in the second shell is 2(in s orbital) +4 (in p orbital) =6.The number of unpaired electrons is 8-6=2
A water molecule has four hydrogen bonds, because it is made up of two hydrogen atoms and an oxygen atom. A water molecule has 10 protons and 10 electrons thus it is neutral. In the water molecule there is formation of covalent bonds where oxygen atom and hydrogen atoms share electrons though the sharing is not equal. In the covalent bond, the oxygen atoms attract electrons more than the hydrogen atoms.
 
        
                    
             
        
        
        
I think the correct answer from the choices listed above is option A. Sickle cell disease is caused by a change in allele. It is a disorder of the blood caused by an inherited abnormal hemoglobin. Hope this answers the question. Have a nice day.
        
             
        
        
        
Answer:
Answer: Water rise to tall trees by suction pull during day it is low but during night time it is fast. during night time transpiration is fast and transpiration create a pressure also called transpirational pull which cause root water to move at leaves.
Explanation:
 
        
                    
             
        
        
        
Answer:
A = Activator
B = Effector
Explanation:
An activator is a protein which typically binds to a short (50–1500 bp) region of DNA which might be located either upstream (mainly) or downstream of a gene so as to cause increased transcription. This particular region of DNA is known as enhancer and activator is also  known as transcription factor. Activator is a trans-acting factor which binds to the cis-acting factor which is enhancer so as to enhance transcriptional expression. 
But another protein named as effector may restrict activator from binding to the enhancer leading to a decrease in transcriptional expression by binding to the activator allosterically. Allosteric binding of effector to the activator causes conformational change in activator so it can no longer bind the enhancer. 
 
        
             
        
        
        
Limiting factors for snakes can include frogs, grasshoppers, farmers, pesticides, weather, climate, the environment, and various other abiotic and biotic factors.
Those specified however were also specified within the prompt. These are limiting factors because they can limit or help excel the snake population growth, yet in this prompt it is shown to greatly diminish the growth.
Hope this helps!