Again great job! They all look correct except 20. is 3.7 due to sig fig of least precision, which you have a mark by!! You don't even need help!;) Here comes the next chemical engineer! :)
I've actually used the magnet test to determine if a gold necklace of mine was real or not. If the gold item aka the crown is attracted to a magnet, it is definitely not real gold.if it isn't then its real gold.
Answer:

Explanation:
We usually approximate the density of water to about
at room temperature. In terms of the precise density of water, this is not the case, however, as density is temperature-dependent.
The density of water decreases with an increase in temperature after the peak point of its density. The same trend might be spotted if the temperature of water is decreased from the peak point.
This peak point at which the density of water has the greatest value is usually approximated to about
. For your information, I'm attaching the graph illustrating the function of the density of water against temperature where you could clearly indicate the maximum point.
To a higher precision, the density of water has a maximum value at
, and the density at this point is exactly
.
there is more air near sea level