Question

Quarks are thought to be the building blocks of protons. Which was most affected by the discovery of the quark?
the estimated mass of a proton
the observation that protons have a +1 charge
the view that the atom cannot be broken down further than protons
the theory that the nucleus of an atom contains protons and neutrons

Answer 1

the view that the atom cannot be broken down further than protons

Explanation: quarks showed that protons (and neutrons) have internal structure — they are made of quarks — so atoms can be divided beyond protons. The proton's +1 charge and the existence of nuclei with protons/neutrons remained valid; mass estimates were refined but less fundamentally changed.