### 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$
Part of INC-05 — s-Block Elements
Quick Revision: INC-05 Most Important Points
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