I think answer is
C. Something that can be observed or measured while changing the identity of the substance
Answer:
Water ______________________________________________
For radioactive decay, we can relate current amount, initial amount, decay constant and time using:
N = No x exp(-λt)
Half-life = ln(2)/λ
λ = ln(2) / 5730
N/No = 80% = 0.8
0.8 = exp( -ln(2)/5730 x t)
t = 1844 years
Ice floats after it crystallizes because ITS DENSITY IS LESS THAN THAT OF WATER.
When a quantity of water is cools down by reducing its temperature, the molecules of the water lose kinetic energy and slow down in their movement. As the water is cooling down, it is volume is expanding. When the temperature reaches zero degree Celsius, the water becomes ice. At this point, the ice can float on water because its density is less than that of water; this is as a result of the spaces that now exist in the ice structure.
