s-Block elements include Group 1 (alkali metals, $ns^{1}$) and Group 2 (alkaline earth metals, $ns^{2}$), which are the most electropositive metals in their respective periods. Down each group, atomic radius increases, ionization enthalpy decreases, and reactivity with water increases. Alkali metals produce characteristic flame colors: Li (crimson), Na (golden yellow), K (violet), Rb (red-violet), Cs (blue). When burned in excess oxygen, Li forms the normal oxide $Li_{2}O$, Na forms the peroxide $Na_{2}O_{2}$, and K/Rb/Cs form superoxides due to the stabilization of larger anions by larger cations. Lithium shows a diagonal relationship with magnesium, sharing properties such as forming only the normal oxide, carbonate decomposition on heating, and $LiNO_{3}$ decomposing like Mg($NO_{3}$)_{2}. NaOH is manufactured by the Castner-Kellner cell (mercury cathode electrolysis of brine), while $Na_{2}CO_{3}$ is made by the Solvay process in which $NaHCO_{3}$ precipitates due to its lower solubility. Beryllium is anomalous in Group 2, forming an amphoteric oxide and covalent chlorides, and shows a diagonal relationship with aluminium. Plaster of Paris ($CaSO_{4}$·½$H_{2}O$) sets by hydrating to gypsum ($CaSO_{4}$·2$H_{2}O$) in an exothermic reaction with slight expansion. $Na^{+}$ and $K^{+}$ control nerve impulse transmission and osmotic balance, $Mg^{2+}$ is the central atom in chlorophyll, and $Ca^{2+}$ forms hydroxyapatite in bones and teeth. The most NEET-critical facts are the oxide type trend in Group 1, the Solvay process precipitation logic, and the five shared properties of the Li-Mg diagonal pair.