2H₂ + O₂ → 2H₂O is a combination reaction where two or more reactants combine to form a single product. A is decomposition. C is displacement. D is neutralization (also double displacement). Combination reactions are generally exothermic. Another example: C + O₂ → CO₂.
Consider the following statements about the modern periodic table: 1. Elements are arranged by atomic mass. 2. It has 18 groups and 7 periods. 3. The f-block elements are called inner transition metals. Which are correct?
Explanation:
The modern periodic table is based on atomic number, not atomic mass (Mendeleev's table was based on mass). It consists of 18 vertical groups and 7 horizontal periods. The f-block elements, placed at the bottom, are indeed called inner transition metals (lanthanides and actinides). Thus, statements 2 and 3 are correct.
Explanation:
Using Boyle's law: P₁V₁ = P₂V₂ => 2 atm × 5 L = 1 atm × V₂ => V₂ = 10 L. As pressure decreases, volume increases. The same mass of gas expands. This is a direct application of inverse proportionality. If temperature and amount of gas are constant, doubling pressure halves volume, etc.
Explanation:
Stainless steel contains iron, chromium (min 10.5%), and often nickel. Chromium forms a passive oxide layer preventing rust. Nickel improves ductility and corrosion resistance. Molybdenum may be added for pitting resistance. Brass is Cu-Zn, bronze is Cu-Sn, solder is Pb-Sn.
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