Chemistry MCQs for NEET — Practice Questions with Answers

The text states, 'Obviously ionic bonds will be formed more easily between elements with comparatively low ionization enthalpies and elements with comparatively high negative value of electron gain enthalpy.'

The limitations listed are: '• It is clear that octet rule is based upon the chemical inertness of noble gases. However, some noble gases (for example xenon and krypton) also combine with oxygen and fluorine to form a number of compounds like XeF$_2$, KrF$_2$, XeOF$_2$ etc. • This theory does not account for the shape of molecules. • It does not explain the relative stability of the molecules being totally silent about the energy of a molecule.' The octet rule does fail to explain incomplete octets, so this is a limitation, not a non-limitation. The statement that it suggests noble gases are always inert is incorrect; their inertness is the basis, but exceptions exist, making this a limitation rather than a non-limitation that is 'always true.'

According to the NCERT calculation for ozone (O$_3$): 'The formal charge on: • The central O atom marked 1 = 6 – 2 – 1/2 (6) = +1'. Here, 6 is the valence electrons of O, 2 are lone pair electrons, and 6 are bonding electrons (3 shared pairs).

The text states, 'G.N. Lewis, an American chemist introduced simple notations to represent valence electrons in an atom. These notations are called Lewis symbols.'

The text states: 'The valence bond (VB) approach to covalent bonding is basically concerned with the energetics of covalent bond formation about which the Lewis and VSEPR models are silent. Basically the VB theory discusses bond formation in terms of overlap of orbitals.'

The context mentions: 'For example the formation of the $H_2$ molecule from two hydrogen atoms involves the overlap of the 1s orbitals of the two H atoms which are singly occupied.'

The text states: 'Because of orbital overlap the electron density between the nuclei increases which helps in bringing them closer.'

The context states: 'For explaining the characteristic shapes of polyatomic molecules Pauling introduced the concept of hybridisation of atomic orbitals.'

The text explicitly mentions: 'Valence bond theory was introduced by Heitler and London (1927) and developed further by Pauling and others.'

The passage lists: 'A discussion of the valence bond theory is based on the knowledge of atomic orbitals, electronic configurations of elements (Units 2), the overlap criteria of atomic orbitals, the hybridization of atomic orbitals and the principles of variation and superposition.' Lattice energy is related to ionic compounds, not explicitly the basis for VB theory presented here.