(i)The mass number of an element is 2.5 times to that of its atomic number if number of nuetron is 120 the atomic number and mass number of element are(ii)A new element Ty(Tyserium) has recently been discovered and consists of 2 isotopes.One isotope has mass 331 g/mol and is 35%abundant.the other isotope is 337 g/mol and is 65% abundant.What is mass of it(iii)how many electrons protons and neutrons are present in 0.18 g of P of mass 30 amu and atomic number 15please tell all questions with detailed steps and prope rexplanation

1
by rajusetu

2014-11-16T09:52:45+05:30
[i]

Let the atomic number be Z
Then the corresponding mass number will be A =>  2.5Z

No of neutrons is given by (A-Z)

Therefore,

A - Z =120
2.5Z - Z = 120
1.5Z = 120
Z= 80

And A = 2.5(80) =200

Hence,
Mass no is  200 and atomic number is 80.

[ii]
The mass number of  the element would be
(35/100)*331 + (65/100)*337
=334.8 g/mol

[iii]
Every mole contains  N_{a} atoms
Every atom contains 15 protons, neutrons and electrons. (since A-Z is also 15)
Hence 30g contain 15* N_{a} particles
So, 0.18 g contains

Which is equal to 0.55 *

I DID NOT UNDERSTAND (III) PART