Correct Answer: mat

Solution : Given:
1. blue black green grey pink ⇒ mat fat tat bat gat
2. grey white orange green ⇒ hat gat nat fat
3. orange green pink grey ⇒ fat nat gat bat
4. violet blue red ⇒ tat lat dat

By comparing all the four coded sentences, we find that –
In sentences 1 and 2, grey and green are common words and gat and fat are common codes.
In sentences 1 and 3, pink and bat are common.
In sentences 1 and 4, blue and tat are common.
The remaining words and codes in sentence 1 are black and mat , in sentence 2 are white , orange and hat , nat , and in sentence 3 are violet , red and lat , dat .

So, black will be coded as mat . Hence, the fourth option is correct.