A spherical ball of radius 7 cm contains 56 w % iron. Find out the number of moles of iron present approximately in the ball ?
( `d=1.4 g cm^(-3)`, atomic mass `= 56 g "mol"^(-1)` )

Options

A. 15.1
B. 20.1
C. 25.1
D. 35.1

Answer

B

Explanation

56 w% iron spherical ball has radius `= 7 cm`
Volume`= 4/3 pi r^(3)= 4/3xx3.14xx(7xx7xx7)`
`d=1.4g//cm^(3)`
Atomic mass `= 56 g//mol`
`n=(d xx10xx"mass"%xx"volume")/("atomic mass" xx 1000)`
`n=(1.4g//cm^(3)xx10xx56xx4/3xx3.14xx(7)^(3))/(56xx1000)`
`n=20.1` mol
Hence, option (b) is correct.