Which of the following reactions are exothermic?

 

$$\begin{gathered} 1) C + O2 → CO2 \\ 2) 2Mg + O2 → 2MgO \\ 3) CuSO4 + 5H2O → CuSO4.5H2O \\ 4) All the above \end{gathered}$$

The gram formula mass is nothing but molar mass.

Composition :

Symbol      Element       Atomic weight       Atoms
   

     P         Phosphorus       30.973762               1       = 30.973
   

     O         Oxygen             15.9994                  4       =  63.998
   

     N         Nitrogen            14.0067                  3       =  42.020
   

     H         Hydrogen          1.00794                  12      =  12.096

Total   =  30.973+63.998+42.020+12.096 = 149.087

The process of conversion of milk into curd is called fermentation.  It is a chemical change. Milk consists of globular proteins called casein. As the microorganism lactobacillus react with milk and turn it to curd. For it 37 degree temperature is needed. But sometimes when it does not get favourable condition, then other microorganism react and makes the curd taste different.

CF4 is tetrahedral.

Since the four 'F' atoms have the same electronegativity values, there is no bias in electron distribution toward any one.

Therefore, electron/charge distribution is symmetrical, which also means that the molecule is nonpolar.

Hence, CF4 is nonpolar molecule with a symmetrical distribution of charge.

What is Dipole :

when two atoms in a molecule have substantially different electronegativity: One atom attracts electrons more than another, becoming more negative, while the other atom becomes more positive.

In chemistry, a metal is an element that readily forms positive ions (cations) and has metallic bonds. Metals are opaque, lustrous elements that are good conductors of heat and electricity. Most metals are malleable and ductile and are, in general, denser than the other elemental substances.

Examples of metals are aluminium, copper, iron, tin, gold, lead, silver, titanium, uranium, and zinc.

Here Se - Selenium is an element but is not a metal, S - Sulphur is not a metal and I - Iodine is also not a metal.

Hence, Zn - Zinc is the only metal in the given options.

The term gram formula mass is synonymous with molecular mass. So, to get this, we must add molar mass of all the elements in this compound.

Given compound is Lithium Sulphate - Li2SO4

Elemental calculation ::

Li  -  Lithium   -   6.941    -     2   -   13.88200 %
S  -  Sulfur     -    32.065   -    1   -   32.065 %
O  -  Oxygen   -   15.9994  -    4   -   63.9976 %

Now, total = 12.6264 + 29.1647 + 58.2090 = 109.9446 

Hence, the gram formula mass of Li2SO4 = 109.9446.

You have to consider three things.

1. First, are the bonds polar?

Look at differences in electronegativity and if  it is >0.5, bonds are polar.

2. Second, does the molecule have unshared electron pairs?

If so, they generally lead to a polar molecule.

3. Third, is the molecule symmetric?

If so, then although the bonds may be polar, the symmetry cancels out the individual bond polarity and the molecule is non polar.

CF4 follows all the rules above and has a symmetric distribution of charge, making it nonpolar. The others all have asymmetric charge distributions.

Hence, CF4 represents a Non-polar molecule.