The ozone layer protects us from: MCQ with Answer and Explanation

Explanation:
Soap solution is basic, pH > 8.3, so it turns phenolphthalein pink. Lemon juice (citric acid) and vinegar (acetic acid) are acidic, pH < 7, phenolphthalein remains colorless. Hydrochloric acid is strongly acidic, colorless. Phenolphthalein indicator is colorless in acidic and neutral, pink in alkaline solutions. It is used in titrations.

Explanation:
Diamond is a giant covalent structure where each carbon is tetrahedrally bonded to four others via strong covalent bonds. Melting requires breaking numerous strong bonds, needing very high temperature (~3500°C). Graphite also has high melting point. Molecular solids like ice have low melting points. Carbon alone doesn't guarantee high m.p.; it's the structure.

Explanation:
Metalloids (B, Si, Ge, As, Sb, Te) are located along the staircase line on the right side of the p-block, dividing metals from non-metals. They exhibit intermediate properties: semiconductors, brittle, can form alloys. They are in groups 13-17. The s-block contains reactive metals. Group 18 contains noble gases. f-block contains lanthanides and actinides.