Question

what is the charge of u quark and write quark representation for neutron?

Answer 1

The charge of u quark is +2/3
neutron is composed of one up quark and two down quarks
n--> u + 2d  
Where n is the neutron, u is the up quark and d is the down quark
The total charge of u + 2d = +2/3 + 2 * (-1/3)
= 2/3 + 2/3 = 0, which is the charge of neutron
Note:Besides the charge the quarks have another property called color. For nuetron, the up quark is red in color and the down quarks are blue and green such that all these colors add up to white. Only particles with white color can remain in isolation.