Answer:
a)
From VSPER theory, the compound TeF₄ and TeCl₄ AX₄E type of models. Hence, the molecular geometry of this molecule is trigonal bipyramidal. The plausible structure of this molecule are shown on the first uploaded image
Looking at the image we see that structure 1 has three lone pairs repulsion with 90° angle. From VSPER theory, the repulsive force between the electron pair is given as
lone pair - lone pair > lone pair - bond pair > bond pair - bond pair
The above shows that bond pair -bond pair has less repulsion than lone pair- bond pair, and next is lone pair - lone pair
This means that structure 2 is more stable structure for TeF₄ or TeCl₄ .,because the lone pair is present at equatorial position.
This stable structure is shown on the second uploaded image
A lone pair of electron occupy more space around the central atom than a bond pair electron that are present at axial positions, the two atoms that are present at axial position are tilt away from the lone pair
We can see the structure on the third uploaded image
Due to the repulsive interaction , the bond distance between Te - X(axial) increases, which means that the Te - X(axial) distance is longer than Te - X(equitorial) distance.
b)
It is a general concept that TeX₄ ha a bond angle of 90° for axial position and 120° in between equitorial position. This is shown on the fourth uploaded image
Considering TeF₄ and TeCl₄ , F is more electro-negative element Than Cl.This mean that the fluorine would pull strongly the shared electron away from the Te which reduces the electron density near the central Te atom.This would result in decrease bond angle be TeCl₄
So , F(axial) - Te - F(axial) has smaller bond angle than Cl(axial) - Te - Cl(axial)
Considering the equitorial position we see that because of the highly electro - negative fluorine atom, the bond angle decrease much in TeF₄ than in TeCl₄
This means that F(equitorial) - Te - F(equitorial) has smaller bond angle than Cl(equitorial) - Te - Cl(equitorial)
