We have 30% (w/w) HCl this means :
100 g solution contains 30 g HCl
?? g solution contains 7.5 g HCl
By cross multiplication:
Mass of solution =

= 25 g solution
You can define an element as a substance with only one type of atom in
(e.g. only sulphur atoms). If a substance has more than one type of atom
in, then it is either a compound or a mixture, depending on whether the
elements have bonded. Examples of elements are:
Oxygen
Sulphur
Carbon
Hydrogen
Protactinium
Compound-
A substance made up of atoms of two or more different elements joined by chemical bounds.
Molecule- a pure substance that cannot be broken down
Salt- A Ionic Compound Formed From The Reaction Of An Acid And Base .
<span>Active transport runs counter to facilitated diffusion. In active transport, molecules move against the concentration gradients, running from areas of lower concentration to areas of higher concentration. This is where energy is used.</span>
Answer:
a) Sm
Explanation:
Hello,
This substantiation could be done by knowing how to compute the released energy for 1 mol the oxide. Thus, for Sm, the computation turns out into:

The sign just indicates that the heat is released due to the chemical reaction and it matches with the indicated heat in the statement.
Best regards.