Question

The soldiers of Napoleon army while at Alps during the freezing winter suffered a serious problem as regards the tin buttons of their uniforms. White Metallic tin buttons get converted to grey powder. This transformation is related to:
A) an interaction with water vapour contained in humid air
B) a change in crystalline structure of tin
C) a change in the partial pressure of ${O_2}$ in air
D) an interaction with ${N_2}$ of air at low temperature

Answer 1

Let us first try to analyse the question. It is given that there’s freezing winter condition which means the temperature is very low and it is given that the white metallic tin gets converted into grey powder due to the temperature change.

Complete step by step solution:
Tin has different allotropic forms at different conditions, so when we consider white tin it is called as $\beta - Sn$ ( $Sn$ is how we represent tin in periodic table) and the grey powder tin is known as $\alpha - Sn$ . At around ${13^ \circ }C$ $\beta - Sn$ gets converted into $\alpha - Sn$ . Now due to temperature change there is a change in crystalline structure. $\beta - Sn$ which is white metallic in nature has tetragonal crystal structure and also has greater density with close packing of whereas in $\alpha - Sn$ it has cubic crystal structure which has low density and which is obtained in the form of grey powder
So, as there is no interaction with ${N_2}$ option D cannot be true. There is no interaction with water vapour hence we can eliminate option A. and there is no condition given in question which talks about pressure change.
Hence, the correct option is B.

Note:
Tin is mainly used as coating for zinc, lead and steel to protect from corrosion, it is also used to solder for joining pipes or electric circuits and also has a wide range of use in chemical applications. Only $\beta$ tin is useful $\alpha$ tin has no particular use till now.