In a certain code language, 'PENCIL' is written as 'CEILNP' and 'FROS…

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The logic followed here is;

(letters are arranged in the order they appear in the english alphabet series)

So, that's how PENCIL is arranged as CEILNP

And,

'FROST' is written as 'FORST'

Similarly, 'DUSTBIN' be written as BDINSTU