Oxide type confusion: Do not memorize only "$Li_{2}O$, $Na_{2}O_{2}$, $KO_{2}$" without the reasoning. The trend is: small cation → small anion (oxide $O^{2-}$), large cation → large anion (superoxide $O_{2}^{-}$). If you forget K, apply the logic: $K^{+}$ is large → superoxide.

Solvay process trap: $NaHCO_{3}$ precipitates because it is less soluble than $NH_{4}Cl$, not because it is the first product to form. The question is frequently worded to catch this exact misconception.

$LiNO_{3}$ vs. $NaNO_{3}$ decomposition: $LiNO_{3}$ gives $Li_{2}O$ + $NO_{2}$ + $O_{2}$ (same as Mg($NO_{3}$)_{2}). $NaNO_{3}$ gives Na$NO_{2}$ + $O_{2}$. Do not apply the Mg/Li pattern to the rest of the alkali metals.

Li does NOT form solid $LiHCO_{3}$: It exists only in solution. Do not write $LiHCO_{3}$ as a product of C$O_{2}$ + LiOH unless the question specifies solution.

Be is NOT basic — it is amphoteric: Unlike all other Group 2 metals whose oxides are basic, BeO dissolves in both NaOH and HCl. Confusing Be with Ca, Mg, Ba is a common error.

$BeCl_{2}$ geometry: In the gaseous monomer, $BeCl_{2}$ is linear (sp hybridized, electron-deficient). In solid state, it is polymeric. Do not apply VSEPR to the polymeric form.

Plaster of Paris formula: $CaSO_{4}$·½$H_{2}O$ — the ½ water of crystallization is critical. Writing $CaSO_{4}$·$H_{2}O$ is incorrect. The formula is sometimes written as ($CaSO_{4}$)_{2}·$H_{2}O$ for two formula units.

Castner-Kellner vs. chlor-alkali: Both electrolyze brine. The Castner-Kellner cell uses a mercury cathode; the modern membrane cell/diaphragm cell (chlor-alkali process) is different. Do not conflate them.

$Li^{+}$ hydration: Despite being the smallest alkali metal ion, $Li^{+}$ has the largest hydrated ionic radius and the highest hydration enthalpy because the small bare ion attracts water molecules very strongly.

Diagonal relationships are between group and period: Li resembles Mg (one group right, one period down). Be resembles Al. These are not within the same group or same period.