Marie curie worked as a governess and she was awarded noble prize for her discoveries.
Explanation:
When Marie curie worked as a governess for three years her employer allowed her to teach reading to the children of peasant workers at his beet sugar factory. This was banned under Russian rule. During that time she studied chemistry lessons from her father by mail.
Marie curie was awarded the Noble prize in chemistry for her discoveries and studies of elements radium and polonium. She is the only women who is awarded the Noble prize twice.
She made her first research into the treatment of tumors with radiation and founded a Curie institutes, that are important medical research centers.
7.91 g/ml is the density of the iron piece of 28.5 gms.
Explanation:
The density of a substance is defined as the volume it occupies. It tells the matter present in a substance.
The density is mass per unit volume and is denoted by p.
The formula for density is given by:
density (p) = 
Data given is :
mass= 28.5 grams
V1 = 45.5 ml
V2= 49.1 ml
The initial volume of water was 45.5 ml, when iron piece of 28.5 grams was added the final volume was 49.1 ml.
Putting the values in the equation of density
p = 
p = 7.91 g/ml
Since iron is a dense material it will occupy less volume
<span>Avogadro's number.
1 mole of any substance, molecule or element is equal to a certain amount of atom.
6.022 x 10^23 is the Avogradro's constant.
Magnesium Oxide is a compound. therefore if you have 30.3 g of it (1 mol), it will have the same number of atoms.
34.69 moles of MgO has 208.9 x 10^23 number of atoms.
2.089 x 10^25 is also a correct answer.</span><span>
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