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 most important polymer present in the nucleus is DNA- the master molecule. It is a polymer of Nucleotides.

'M' is used as a unit of molarity and stands for mole per litre i.e, number of moles of solute per liter of solution.

A concentrated solution will contain the most solute molecules per solvent molecules.

Here in the given options,

1)  6/10 = 0.6

2) 20.5/50 = 0.41

3) 30/120 = 0.25

4) 2.6/2 = 1.3

Hence, option D) is most concentrated.

Henry's Law tells that the solubility of a gas is directly proportional to the partial pressure of the gas above the solvent. Hence under high pressure, more gas is dissolved.

Also that Henry's Law involves a constant which is temperature-dependent. Under high temperatures, less gas is dissolved whereas under low temperatures, more gas is dissolved.

For Example ::  

You can think of a can of soda. The contents are under pressure and if you shake the can before opening, the soda fizzes out all over as you open it. So the higher the pressure, the more gas or more CO2 can be dissolved in the drink.

Eliminate choices 1 and 2. Now focus on the temperature. Soda goes flat (loses carbonation or gas) as it warms up. Soda is usually served cold because more of the carbonation or CO2 stays in the drink when the soda is cold.

Hence, in high pressure and low temperature conditions gases are most soluble in water.

Any two amino acids vary structure by the r-group, otherwise all amino acids are in the same structure. All amino acids have in common carboxyl group -COO , amino group -NH3+ and a hydrogen -H and a r-group which are all bonded to a central carbon.

Covalent bonds hold atoms together because the attraction between the positively charged nuclei and the negatively charged shared electrons is greater than the repulsions between the nuclei themselves.

Colored aqueous solutions are a characteristic of transition compounds.

The only transition compound in the above choices is CrCl3.

Cr is a transition element.

The name given to the bond between water molecules is a hydrogen bond. These bonds occur between the slightly negative oxygen of one water molecule and the slightly positive hydrogen of another water molecule. Hydrogen bonding gives water special physical properties.

The differences in electronegativity between hydrogen and oxygen lead to an unequal sharing of electrons. Electronegativity measures how strongly an atom attracts electrons. Oxygen, with its higher electronegativity, pulls on the shared electrons more, giving the oxygen atom a partial net negative charge. The shared electrons spend less time with the hydrogen atoms; therefore, the hydrogen regions of water have partial positive charges.