There are three quarks you need to know: up, down and strange

Quarks, Leptons & Conservation Laws — AQA A-Level Physics

Quarks are fundamental particles that combine to form hadrons.
At A-Level, you need three quarks: up ($u$), down ($d$) and strange ($s$).
Each quark has a corresponding antiquark with opposite chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C)., baryon numberA quantum number conserved in all interactions. Baryons (protons, neutrons) have baryon number +1, antibaryons have -1, and mesons/leptons have 0. and strangeness.

Quark properties

Quark	Symbol	Charge	Baryon Number	Strangeness
Up	$u$	$+\frac{2}{3}$	$+\frac{1}{3}$	$0$
Down	$d$	$-\frac{1}{3}$	$+\frac{1}{3}$	$0$
Strange	$s$	$-\frac{1}{3}$	$+\frac{1}{3}$	$-1$
Anti-up	$\bar{u}$	$-\frac{2}{3}$	$-\frac{1}{3}$	$0$
Anti-down	$\bar{d}$	$+\frac{1}{3}$	$-\frac{1}{3}$	$0$
Anti-strange	$\bar{s}$	$+\frac{1}{3}$	$-\frac{1}{3}$	$+1$

Quark composition of common particles

Particle	Symbol	Quark Content	Charge	Strangeness
Proton	$p$	$uud$	$+1$	$0$
Neutron	$n$	$udd$	$0$	$0$
Pion +	$\pi^{+}$	$u\bar{d}$	$+1$	$0$
Pion −	$\pi^{-}$	$\bar{u}d$	$-1$	$0$
Pion 0	$\pi^{0}$	$u\bar{u}$ or $d\bar{d}$	$0$	$0$
Kaon +	$K^{+}$	$u\bar{s}$	$+1$	$+1$
Kaon −	$K^{-}$	$\bar{u}s$	$-1$	$-1$
Kaon 0	$K^{0}$	$d\bar{s}$	$0$	$+1$

Common Mistake MEDIUM

Students often: Assigning strangeness $= +1$ to the strange quark.
Instead: The strange quark has strangeness $= -1$. The anti-strange quark has strangeness $= +1$. Particles containing $s$ have $S = -1$ (e.g. $K^{-}$, $\Lambda^{0}$). Particles containing $\bar{s}$ have $S = +1$ (e.g. $K^{+}$).

Related:Particle Interactions