Answer:
A pure substance has a sharp melting point (melts at one temperature) and a sharp boiling point (boils at one temperature). A mixture melts over a range of temperatures and boils over a range of temperatures. Homogeneous mixtures are called solutions.
The ANSWER is D
salt In water because it is a simple ion pair Na+1 and Cl-1
Hydrogen Fluoride is similar: H+1 and F-1 and since it is a polar ion pair too it dissolves in water
Molecules in solids are packed a lot closer together than molecules in liquids and gases, so there is far less space between solid particles. Because of this, solid particles cannot move around quickly and freely like liquids and gases, instead they only vibrate so are fairly 'locked' into the same place, so solids have fixed volume and space.
The building block of matter are atoms
7.91 g/ml is the density of the iron piece of 28.5 gms.
Explanation:
The density of a substance is defined as the volume it occupies. It tells the matter present in a substance.
The density is mass per unit volume and is denoted by p.
The formula for density is given by:
density (p) = 
Data given is :
mass= 28.5 grams
V1 = 45.5 ml
V2= 49.1 ml
The initial volume of water was 45.5 ml, when iron piece of 28.5 grams was added the final volume was 49.1 ml.
Putting the values in the equation of density
p = 
p = 7.91 g/ml
Since iron is a dense material it will occupy less volume
