Let's analyze the highlighted parts:

1. **discus**s**ion** - The highlighted "s" is pronounced as /ʃ/ (sh sound).
**deci**s**ion** - The highlighted "s" is pronounced as /ʒ/ (zh sound).
**trea**s**ure** - The highlighted "s" is pronounced as /ʒ/ (zh sound).
**vi**s**ion** - The highlighted "s" is pronounced as /ʒ/ (zh sound).

The word with a different sound is **discussion** because the highlighted "s" is pronounced differently as /s/.

2. **simil**a**rity** - The highlighted "a" is pronounced as /ə/ (schwa sound, like in "sofa").
**t**a**lent** - The highlighted "a" is pronounced as /æ/ (as in "cat").
**h**a**ppy** - The highlighted "a" is pronounced as /æ/ (as in "cat").
**h**a**rd** - The highlighted "a" is pronounced as /ɑː/ (as in "hard").

The word with a different sound is **similarity** because the highlighted "a" is pronounced as /ə/ (schwa sound), which is different from the other three.

**Summary:**
1. **Discussion**
2. **Similarity**