MASS= Density times Volume
2.70*405
M= 1093.5
A melting point of over 700 C and a density of less than 2 g/cm3 can be observed for many group 2 elements. In this group, the density increases on moving down the group, whereas the melting point increases upto calcium and then starts decreasing.
Calcium, symbol Ca is the element with melting point around 840 C and density of 1.55 g/cm3 which is closest to the specified data range .
The trend will be such that the time taken for the cross to disappear will be increasing.
<h3>Rate of reactions</h3>
The rate of reactions is affected by the concentration of reactants. The more concentrated the reactants are, the more the rate of the reaction, and vice versa. This is based on the condition that all other factors are kept constant.
In the illustrated reaction, the volume of sodium thiosulfate decreases downward while the volume of water increases. This means that the sodium thiosulfate gets more diluted as we move downward.
Thus, the reaction rate will keep decreasing. In other words, more time would be needed for the cross to disappear as the concentration of sodium thiosulfate decreases.
More on concentration and rate of reactions can be found here: brainly.com/question/13764840
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