Potassium-40 has a half life of 1.251×billion<span> years</span><span>. To determine the percentage potassium-40 remaining after 3.9 billion years, divide
3.9 by 1.251, = 3.12.
This is the number of times the original amount of potassium-40 reduces by 50%. The remaining percentage is therefore 100%/(3.12 * 2) = 16.03%.</span>
        
             
        
        
        
2 and 3 are too similar to distinguish because they both are saying it's been back up on several different accounts but 3 seems like a more solid answer go with 3
        
             
        
        
        
Answer:
Ca has 20 protons, so neutral it would have 20 electrons, but according to the charge, 2 electrons have been lost.
Explanation:
 
        
             
        
        
        
Answer:
The answers to both parts (1 and 2) are given below.
Explanation:
1. The calorimeter is similar to the bomb calorimeter in a way that both measure the changes in heat that occur as result of the chemical reaction taking place inside them. They are different in the sense that a bomb calorimeter provides an isolated system with constant volume and pressure, whereas a regular calorimeter allows pressure to equalize with the environment.
2. Carbohydrates are the molecules that break down and provides energy for cellular functions. Whereas, proteins are not meant for the production of energy but for the production of amino acids to function as structural units for protein synthesis. Simply, the breakdown of protein is for the synthesis of more proteins by providing several units of amino acids rather than the production of energy. 
 
        
             
        
        
        
Answer:
xerophytes is a species of plant that has adaptations to survive in an environment with little liquid water such as a desert,ice or snow covered region.
examples are; pineapple and gymnosperm plants.