Among the following the maximum covalent character is shown by the compound

(1)MgCl2

(2)FeCl2

(3)SnCl2

(4) AlCl3

SiCl4 is a non polar as the forces of attraction between the shared pair of electrons are equal and the molecule is symmetric.

In the periodic table, the atomic radius increases from top to bottom in the groups and it increases from right to left in the periods.

Francium is the atom with largest atomic radius. Helium is the atom with smallest radius.

Activation energy is a minimum amount of energy that required for the chemical reaction to happen or to take place.

The chemical name of common is sodium chloride. Its chemical formula is NaCl.

To get the mass of a mole of NaCl, we need to add the molar atomic weights of the individual elements i.e, Na and Cl

Atomic weights of Na = 22.99 gm/mol  Cl = 35.45 gm/mol

Now, mass of a mole of NaCl = 22.99 + 35.45 = 58.44 gm/mol.

When a muscle is contracted and relaxed some amount of heat is released as a by product. 

Oxygen is the final electron acceptor of cellular respiration.

Here all the given compounds have both ionic and covalent bonds.

NaNO3 - In Sodium nitrate, Nitrate is covalently bonded as nitrogen is bonded with 3 oxygen atoms. And this nitrate is ionically bonded with sodium.

CaSO4 - In Calcium sulphate, sulphate is covalently bonded as sulphur is bonded with 4 oxygen atoms. And this sulphate is ionically bonded with calcium.

NH4Cl - In Ammonium chloride, ammonium is covalently bonded as nitrogen is bonded with 4 hydrogen atoms. And this ammonium is ionically bonded with chlorine.