What happens to the mass number of a nucleus that emits an alpha particle?

The mass number decreases by four.

An α particle is the nucleus of a helium atom, ₂⁴He.

Thus, if a nucleus emits an alpha particle, its mass number decreases by four.

weight of any object is given by

w = m*g

where m is mass of the object and g is the acceleration due to gravity.

for earth the value of g is 9.8 m/s^2 so

w=117.6 n m=12 g=?

117.6=12g => g=9.8 m/s^2

which is the force of gravity on earth.