The lock and key model is used to explain how enzymes work. use this model to explain why an enzyme only works with a particular molecule?

The lock and key model is used to explain how enzymes work.  

Explanation:

An enzyme is a protein  that functions as a biological catalyst . Enzymes are folded into complex shapes that allow smaller molecules to fit into them. The place where these molecules fit is called the active site.

The lock and key model was given by Emil Fischer in 1984 . According to this model  the active sites of the enzymes have a specific geometric shapes wherein the substrate molecules fit in just like a key in a particular lock.

The lock and key model of an enzyme action is based upon structural complimentarity  between the substrate molecule and the enzyme active   site . Thus specific enzyme molecules will interact with specific substrate molecules only .

This specific action of an enzyme with a single substrate can be explained using lock and key analogy . In this analogy  the lock is the enzyme and the key is the substrate . Only correctly  sized key ( substrate ) fits into the key hole ( active site ) of the lock ( enzyme )  

a

explanation:

- calcium has greater affinity to bond with electron receptors than hydrogen does and hence, it has the ability to replace hydrogen in most of its compounds.

- lithium has 2 valence electrons in the product because it can make only 1 bond with hydrogen. beryllium has 4 valence electrons in the product because it can only make 2 bonds. it has fewer electrons than neon and can react with electron donors. each hydrogen has 2 valence electrons, the same as helium.

- the covalent bond formed between carbon and hydrogen is polar because carbon is more electronegative than hydrogen and it attracts the bonded electron pair closer to itself, thus giving hydrogen a partial positive charge.

- a hydrogen bond is a relatively weak bond that hydrogen atoms make with the electronegative atoms nitrogen, oxygen or fluorine.

so the best choice is a.) 2 calcium (ca) atoms