Explain why a glass prism can produce a spectrum when white light passes through it but a glass slab cannot.

In an experiment, a beam of white light gets split into seven colours marked $1$ to $7$ as shown in the figure. The student who carried out this experiment makes the following statement with regard to the experiment:

"The colours, $3$ and $5$ are similar to the colour of the sky and egg yolk respectively." Is this statement correct or incorrect? Justify your answer.

In an experiment, a beam of white light gets split into seven colours marked $1$ to $7$ as shown in the figure. The student who carried out this experiment makes the following statement with regard to the experiment:

Which two positions correspond closely to the colour of (i) danger or stop signal lights; (ii) potassium permanganate solution?