To determine the code for the word HABIT, we need to analyze the given codes for the words HAT and RABBIT.

Given:
HAT is coded as 782
RABBIT is coded as 681192

Let's break down the codes and observe the pattern:

1. Code for HAT (782):
- The word HAT has three letters.
- The code consists of three digits.
- The first digit (7) represents the first letter 'H'.
- The second digit (8) represents the second letter 'A'.
- The third digit (2) represents the third letter 'T'.

2. Code for RABBIT (681192):
- The word RABBIT has six letters.
- The code consists of six digits.
- The first digit (6) represents the first letter 'R'.
- The second digit (8) represents the second letter 'A'.
- The third digit (1) represents the third letter 'B'.
- The fourth digit (1) represents the fourth letter 'B'.
- The fifth digit (9) represents the fifth letter 'I'.
- The sixth digit (2) represents the sixth letter 'T'.

From the given examples, we can observe that the code for each letter is determined by its position in the word. Therefore, the code for the word HABIT can be determined as follows:

- The word HABIT has five letters.
- The code should consist of five digits.
- The first digit should represent the first letter 'H'.
- The second digit should represent the second letter 'A'.
- The third digit should represent the third letter 'B'.
- The fourth digit should represent the fourth letter 'I'.
- The fifth digit should represent the fifth letter 'T'.

Based on this pattern, we can conclude that the code for HABIT is 78192. Therefore, the correct answer is option B: 78192.