Answer:
The reasons can be :
There are impurities in substances
The atomic mass unit, or amu, is 1/12 the mass of one atom of carbon-12. An atomic mass unit has the mass of 1/(6.0221415 * 10^23) grams.
Zksjsksjdjxkkdjdkdkdkfkdikdl117283
CaCI2 is for calcium chloride