Answer:
The safety button doesn't click before the jar has been opened because it shows a sign of freshness. Once you have opened it there is no way to make it click again.
If bacteria gets stored in the jar they will produce gas. If the button does not pop or click after opened that is a sign that it may not be so safe to eat. Clicking shows that there is still vacuum to the jar.
Explanation:
Answer:
Potential energy.
Explanation:
Potential energy is the energy in a body due to its position.
Answer:
4.90 moles of
will produce (9.8) moles of
,
(4.90) moles of
and
(39.2) moles of 
Explanation:
From the question we are told that
The number of moles of is 
The formation reaction of
is
From the reaction we see that
1 mole of
is formed by 2 moles of
1 mole of
and 4 
This implies that
4.90 moles of
will produce (2 * 4.90) moles of
,
(1 * 4.90) moles of
and
(8 * 4.90) moles of 
So
4.90 moles of
will produce (9.8) moles of
,
(4.90) moles of
and
(39.2) moles of 
To predict the solubility of the compounds you should base on solubility tables.
I used one from wikipedia. If you google "solubility table" you will find this table as first option.
There I found that nickel, potassium and sodium chlorides are very soluble with solubilities of two digits. While lead clhoride has a solubility close to 1 g per 100 g of water. Then lead is the ion that will precipitate with certainty.