Solids: have fixed shape and fixed volume
Liquids: have fixed volume
Gases: have neither fixed volume or fixed shape
This tells you that having a fixed shape is the most responsible characteristic of a solid's structure.
There are multiple answers to this question depending on what answer it's looking for. This is one of the right answers but I don't know if it's the one the question is looking for.
Answer:

Explanation:
1. Calculate the moles of NaOH.
2. Calculate the volume of NaOH

It is softer than topaz and and it is softer than diamond (diamond has a Mohs hardness of 10, which is the highest value of the scale)
Answer:
237.2 mL.
Explanation:
- We have the rule: at neutralization, the no. of millimoles of acid is equal to the no. of millimoles of the base.
(XMV) acid = (XMV) base.
where, X is the no. of (H) or (OH) reproducible in acid or base, respectively.
M is the molarity of the acid or base.
V is the volume of the acid or base.
<em>(XMV) HCl = (XMV) NaOH.</em>
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For HCl; X = 1, M = 0.5 M, V = ??? mL.
For NaOH, X = 1, M = 1.54 M, V = 77.0 mL.
<em>∴ V of HCl = (XMV) NaOH / (XV) HCl = (</em>1)(1.54 M)(77.0 mL) / (1)(0.5 M) = <em>237.2 mL.</em>