This is College Physics Answers with Shaun Dychko. The <i>D</i> plus meson has a baryon number, strangeness number, bottomness and topness of zero and since it's a meson, it must have a quark and an anti-quark; only two quark will make it up. It has a charge of plus one we are told and a charm of plus one and we have to figure out what is the quark composition of the <i>D</i> plus meson? Now in order to have a charm of plus one it's very specific what that must mean it must have a charm quark since those are the only types of quarks that have any charm number; everything else is zero here except for this particular row with charm quarks. And it says charm is plus one and so that means the top symbol here refers to the first or the matter column so it means that we have a charm quark in our composition. Now the other quark then has to not have any strangeness, charm, bottomness or topness otherwise those would not be zero and so that means this other quark to go with the charm has to be from one of these two rows here. And we can narrow down which thing it has to be by looking at charge and the charm quark has a charge of positive two-thirds elementary charge and so the other quark that we are gonna pair this term with has to also have a charge of positive one-third and the down-quark has a one-third charge and the anti-down quark is the one that has the positive one-third charge. And so a charm quark and an anti-down quark is the quark composition of the <i>D</i> plus meson.
There are particles called D-mesons. One of them is the $D^+$ meson, which has a single positive charge and a baryon number of zero, also the value of its strangeness, topness, and bottomness. It has a charm of +1. What is its quark configuration?