What is the minimum total energy released when an electron and its antiparticle (positron) annihilate each other?

Solution:

the minimum total energy released when an electron and its antiparticle (positron) annihilate each other is:-

2 mc^2.    [Mass of electron m and c is the velocity of light.]  

m=1*10^(-30) kg., c =3*10^ 8 m/s  

energy released = 2 *9* 10 ^(-14) j  

1 j =6*10^(18) eV.  

Energy released = 6*18*10^4 eV

                               =104*10^4 eV  

                                 =1.04 MeV.

- 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

i'm assuming that the correct answer is indeed the first one/ "a"..