An object of density `12g*cm^(-3)` is weighed with some counterpoising weights made of brass with the help of a common balance. Density of brass = `8g*cm^(-3)`. If the buoyancy of air is neglected in this measurement of mass. Density of air = `1.2xx10^(-3)g*cm^(-3)`.

Explanation

Let the real weight of the body be `mgxxg`, real weight of the brass weights = m. `gxxg`.
Here, apparent weight of the body = apparent weight of the brass weights
or, real weight of the body - weight of air displaced by the body = real weight of the brass weights
or, `m-m/12xx1.2xx10^(-3)=m.-(m.)/8xx1.2xx10^(-3)`
or, `m-mxx10^(-4)=m.-m.xx1.5xx10^(-4)`
or, `(m.)/m=(1-10^(-4))/(1-1.5xx10^(-4))`
or, `(m.-m)/m=((1.5-1)xx10^(-4))/(1-1.5xx10^(-4))=0.5xx10^(-4)`
`therefore"Error"=(m.-m)/mxx100=0.5xx10^(-4)xx100=0.005%`.