Since molarity (M)
\(=\frac {\text{ number of moles of solute} }{ \text{volume of solution in litres } } \)
\(=\frac { \text{ Mass of NaOH Molar mass of NaOH } }{ 0.250L }\)
\(=\frac { 4g/40g }{ 0.250L } =\frac { 0.1mol }{ 0.250l } \)
= 0.4 mol L^-1 = 0.4 M
Note that molarity of a solution depends upon temperature because volume of a solution is temperature dependent.

When n = 5, l = 0, 1, 2, 3. The order in which the energy of the available orbitals 4d, 5s and 5p increases is 5s < 4d < 5p. The total number of orbitals available are 9. The maximum number of electrons that can be accommodated is 18; and therefore 18 elements are there in the 5^th period.

(i) The effective nuclear charge of magnesium is higher than that of sodium. For these reasons, the energy required to remove an electron from magnesium is more than the energy required in sodium. Hence, the first ionization enthalpy of sodium is lower than that of magnesium. However, the second ionization enthalpy of sodium is higher than that of magnesium. This is because after losing an electron, sodium attains the stable noble gas configuration. On the other hand, magnesium, after losing an electron still has one electron.
(ii) Because of stable configuration.

(ii) Markovnikov's Rule: When a polar compound is a unsymmetrical alkene or alkyne, negative part goes to least substituted carbon e.g.,

Molar mass of NH₃ = 14 + 1 x 3 = 17 g mol^-1
Percentage of N \( = \frac{\text{mass of Nin }NH_3} {\text{molar mass of } NH_3} × 100\)
\(=\frac{14}{17}×100\)
= 82.35 %

Mendeleev used atomic weight as the basis of classification of elements in the periodic table. He arranged 63 elements known at that time in the periodic table on the basis of the order of their increasing atomic weight. At some places he ignored the increasing order of atomic weights where the elements having similar properties are placed together.

The ionisation enthalpy of the main group elements decreases regularly on moving down the group due to the following two factors.
(i) Atomic size On moving down the group,atomic size increases due to the addition of new higher energy shell.As a result of this, forces of attraction of nucleus for valence electrons decrease and ionisation enthalpy also decreases.
(ii) Screening effect On moving down the group, screening effect or shielding effect increases, so ionisation enthalpy decreases (because forces of attraction between nucleus and electron secreases).

(i) 0.0048 = 4.8× 10^–3
(ii) 234, 000 = 2.34 ×10⁵
(iii) 8008 = 8.008 ×10³
(iv) 500.0 = 5.000 × 10²
(v) 6.0012 = 6.0012

Boiling points of alkanes
1. The boiling points of alkanes rise as the number of carbons increases.
2. Since nonane has a longer carbon chain than octane, it will have a higher boiling point.
Effect of branching on the boiling point of alkane
1. As an alkane chain branch, the surface area of the molecule decreases.
2. The intermolecular force reduces as a result of this.
3. At a lower temperature, the forces can be readily overcome.
4. Therefore, as the branching increases, the boiling point of an alkane chain decreases.

Balance the equation
Balancing the given chemical equation,
N₂(g)+3H₂(g)→2NH₃(g)
Given amount of N₂=2.00×10³g=2000g of N₂ 
Given amount of H₂=1.00×10³g=1000g of H₂
Amount of H₂ required
From the equation, 1 mol (28g) of N₂ reacts with 3 mol(6g) of H₂ to give 2 mol (34g) of NH₂
Mass of H₂ that means with 2000 g of  \(\frac { 6 }{ 28 } \times2000 \)=428.6g of  H₂
Here, N₂ is consumed completely, hence it is the limiting reagent.
Hence, some amount of H₂ will remain unreacted.
Amount of NH₃ produced
Now, 28g of N₂ produces 34g of NH₃
Hence, mass of NH₃ produced by 2000g of N₂= \(\frac { 34 }{ 28 } \) ×2000g NH₃
=2428.57g NH₃
Final Answer: So the mass of ammonia produced is 2428.57g
(ii) Here, N₂ is the limiting reagent and H₂ is the excess reagent. Hence, H₂ will remain unreacted.
(iii) Mass of dihydrogen left unreacted =(1×10³−428.6)g = 571.4g

Electronegativity:
1. The tendency of an atom in a molecule to attract the shared pair of electrons towards itself is known as electronegativity.
2. There is no specific unit for electronegativity. In the modern periodic table:
3. In the modern periodic table: as we move left to right, across a period the nuclear charge increases, atomic size decreases, and electronegativity value increases.
4. As we move down the group there is an increase in the atomic number also nuclear charge and a decrease in the electronegativity value.
5. In general, metal shows a lower electronegativity value compared to on-metals.

(i) (a) Wurtz reaction: When two moles of alkyl halide react with Na metal in presence of dry ether, higher alkanes are formed.

(b) Fittig reaction:


Nucleophilic elimination reaction will take place and 2-methyl propene will be formed.
(iii) Add Tollen's reagent. Ethene will not react. Ethyne will give white ppt. of silver acetylide.