ABSOLUTE MUST-KNOW for NEET 2026

1. Flame Colors (Group 1): Li = Crimson red | Na = Golden yellow | K = Violet | Rb = Red-violet | Cs = Blue

2. Oxide Types (excess $O_{2}$): Li → $Li_{2}O$ (normal) | Na → Na_{2}$$O_{2} (peroxide) | K/Rb/Cs → K$O_{2}$/Rb$O_{2}$/Cs$O_{2}$ (superoxide)

3. Solvay Process Key Facts:

• $NaHCO_{3}$ precipitates because of LOWER SOLUBILITY (not reaction order)
• $NH_{3}$ is recycled using Ca(OH)_{2}
• Final product: Na_{2}$$CO_{3} (washing soda); intermediate: $NaHCO_{3}$

4. Li Anomalous Behavior: $Li_{2}O$ only, no solid LiH$CO_{3}$, Li_{2}$$CO_{3} decomposes, $LiNO_{3}$ → $Li_{2}O$ + N$O_{2}$ + $O_{2}$, LiCl in organic solvents, Li + $N_{2}$ → $Li_{3}N$

5. Be Anomalous Behavior: BeO amphoteric, $BeCl_{2}$ covalent (polymeric solid, $sp^{3}$; linear vapor, sp), max covalency 4, Be dissolves in NaOH

6. Diagonal Relationships: Li ~ Mg (both: normal oxides, decompose carbonates, no bicarbonate solid, LiCl/$MgCl_{2}$ covalent) Be ~ Al (both: amphoteric oxides, covalent chlorides, dissolve in NaOH, max covalency 4)

7. Plaster of Paris: $CaSO_{4}$·½$H_{2}O$ → sets by adding 3/2 $H_{2}O$ → $CaSO_{4}$·2$H_{2}O$ (exothermic, slight expansion ~1%) Temperature: 373 K for POP; above 393 K = dead-burnt (no setting)

8. Portland Cement: $Ca_{3}SiO_{5}$ = early strength | $Ca_{2}SiO_{4}$ = long-term strength | Gypsum = retarder (2-3%)

9. Group 2 Solubility Trends: Sulphates: ↓ decreases down ($BeSO_{4}$ > $BaSO_{4}$) Hydroxides: ↑ increases down (Be(OH){2} < Ba(OH){2})

10. Biological Roles: $Na^{+}$/$K^{+}$ = nerve impulse + osmotic balance ($Na^{+}$-$K^{+}$-ATPase pump) $Mg^{2+}$ = chlorophyll center + enzyme cofactor $Ca^{2+}$ = hydroxyapatite (bones/teeth) + blood clotting + muscle contraction