$$BC{l_3}$$ have $$s{p^2}$$ hybridisation and no lone pair of electron on central atom but $$NC{l_3}$$ have $$s{p^3}$$ hybridisation and also contains one lone pair of
electron on nitrogen, so $$BC{l_3}$$ is planar.
12.
The total number of electrons that take part in forming the bond in $${N_2}$$ is
In $$B{F_3},$$ dipole moment is zero due to its symmetrical structure. Summations of all dipoles is zero.
In $${H_2}S$$ and $${H_2}O$$ due to unsymmetrical structure net $$+ve$$ dipole is there. $${H_2}O$$ has higher dipole due to higher electronegativity of oxygen than sulphur.
14.
$$PB{r_2}C{l_3}$$ can exhibit geometrical isomerism. Geometrical isomers are as follows :
Which of the above mentioned geometrical isomers has/have no dipole$$(s)$$ ?
When a diatomic molecule lost electron, then its bond order may increase or decrease, so its bond energy may decrease or increase.
18.
If a molecule $$M{X_3}$$ has zero dipole moment, the sigma bonding orbitals used by $$M$$ $$\left( {{\text{atomic}}\,{\text{number}} < 21} \right)$$ are
NOTE: Dipole moment is vector quantity
In trigonal planar geometry $$\left( {{\text{for}}\,s{p^2}\,{\text{hybridisation}}} \right)$$ , the vector sum of two bond moments is equal and opposite to the dipole moment of third bond.
19.
In the case of alkali metals, the covalent character decreases in the order
According to Fajans’ rule,
$${\text{Covalent character}} \propto $$ $$\frac{1}{{{\text{size}}\,{\text{of}}\,{\text{cation}}}} \propto {\text{size}}\,{\text{of}}\,{\text{anion}}$$
In the given options,cation is same but anions are different. Among halogens the order of size is
$$\eqalign{
& F < Cl < Br < I \cr
& \therefore {\text{Order of covalent character is}} \cr
& Ml > MBr > MCl > MF \cr} $$
20.
Assuming that Hund’s rule is violated, the bond order and magnetic nature of the diatomic molecule $${B_2}$$ is
Molecular orbital configuration of $${B_2}\left( {10} \right)$$ as per the condition will be
$$\,\sigma 1{s^2},{\sigma ^*}1{s^2},\sigma 2{s^2},{\sigma ^*}2{s^2},p2p_y^2$$
Bond order of $${B_2} = \frac{{6 - 4}}{2} = 1,\,{B_2}$$ will be diamagnetic.