PROBLEM $1(25$ marks$)$

Circle the correct answer:

a$)$ A given lattice has

A unique unit cell

A unique primitive unif cell and is unique non$-$primitive unit cell

A unique primitive unit cell but more than one non$-$primitive unit cells

More than one primitive unit cells and more than one non$-$primitive unit cellis

b$)$ A crystal has a lattice with the following lattice parameters: $a=b=c$ and a$=$f $=Y^{-90.\text{T}\text{h}\text{e}\text{e}\text{r}\text{y}\text{s}\text{t}\text{a}\text{l}\text{w}\text{i}\text{l}\text{l}\text{h}\text{a}\text{v}\text{e}\text{c}\text{u}\text{b}\text{i}\text{c}\text{s}\text{y}\text{m}\text{m}\text{e}\text{t}\text{r}\text{y}\text{T}\text{r}\text{u}\text{e}\text{F}\text{a}\text{l}\text{s}\text{e}\text{?}}$

True

False

c$)$ In the figure you can see four patterms of atoms. Which one of the circle pattems does not form a lattice? Circle the correct answers and justify your answer.

d$)$ The nature of bonding between the chains in a thermoplastic polymeric material is:

van der Waal's forces

covalent bonds

metallic bond