Which of the following contains both ionic and covalent bonds?

Which of the following pairs of ions is isoelectronic and isostructural?

$Me_3B$,$BH_3$,and $BF_3$ are three Lewis acids. Which one of the following is the correct sequence of these acids in order of their increasing acid strength?

Fill in the blanks given below:
$(i)$ The two theories based on the principles of quantum mechanics are ........ and ......... .
$(ii)$ The electronic configuration of carbon in the excited state is ........... .
$(iii)$ Through the combination of atomic orbitals,....... are formed.
$(iv)$ The ${\rm{CH}}_4$ molecule has a .......... shape.

In the electronic structure of $H_2SO_4$,the total number of unshared electrons is

For the following molecules/ions,identify whether the octet rule is obeyed or not obeyed. Provide the reason.
$(1)$ $PCl_5$ $(2)$ $SF_6$ $(3)$ $PF_5$ $(4)$ $NH_4^+$ $(5)$ $BeCl_2$ $(6)$ $NCl_3$