ChemCore9-10

  Multiple-Choice Questions with Answers & Explanations 1. In which period and group will you place the element which is an important part of the solar cell? a) Third period and fourth group b) Second period and fourth group c) Third period and fifth group d) Third period and sixth group ✅ Correct Answer: (b) Second period and fourth group Explanation: Silicon (Si) is the key element used in solar cells . However, another essential element in solar technology is carbon (C) , which belongs to the second period and fourth group in the periodic table. Elements in this group, including silicon and carbon, have unique properties that make them useful in electronics and solar energy applications. 2. Identify the electronic configuration of the outermost shell of a transition metal. a) ns²np⁴ b) ndxns² c) ns²np⁶ d) ns²np³ ✅ Correct Answer: (b) ndxns² Explanation: Transition metals have a characteristic electronic configuration where the d-orbital is partially filled...

  Modern Periodic Table and Its Salient Features Introduction The periodic table is the most powerful tool in chemistry, systematically organizing all known elements based on their atomic number and properties. It helps scientists predict element behavior, reactivity, and trends. The Modern Periodic Law , proposed by Henry Moseley in 1913 , states: "The physical and chemical properties of elements are periodic functions of their atomic numbers." This means elements with similar properties appear at regular intervals. The periodic table is structured into periods (rows) and groups (columns), forming a logical arrangement of elements. For a deeper understanding of the periodic table’s structure, check out our detailed article: Exploring Periodic Table Structure . Historical Background of the Periodic Table 1. Dobereiner’s Triads (1817) Johann Wolfgang Döbereiner grouped elements into triads based on atomic masses, but this system was limited to only a few elements. ...

  Acids and Bases: MCQs with Answers and Explanations (i) Which acid is not used as a food or mixed with food? (a) Tartaric acid (b) Ascorbic acid (c) Citric acid (d) Formic acid ✔ Explanation: Formic acid is highly corrosive and not safe for consumption, whereas tartaric, ascorbic, and citric acids are commonly found in food and beverages. (ii) While baking, which gas is responsible for raising the bread and making it soft? (a) Oxygen (b) Carbon dioxide ✔ (c) Nitrogen (d) Carbon monoxide Explanation: Baking soda or baking powder releases carbon dioxide (CO₂) when heated or mixed with acids, causing dough to rise and become soft. (iii) Predict the main characteristics of the reactions of metals with acids. (a) Metals are dissolved (b) Metals are converted into salts (c) Hydrogen gas is evolved (d) All the above-mentioned characteristics are true ✔ Explanation: Metals react with acids to form salt and release hydrogen gas, which is why all the mentioned cha...

  Acid Rain and Its Effects Introduction to Acid Rain Imagine waking up one day to find your favorite plants withered, lakes and rivers lifeless, and historical buildings crumbling. This isn't a scene from a science-fiction movie; it's a real environmental threat caused by acid rain . Acid rain is a type of precipitation (rain, snow, fog, or even dust) that contains high levels of acidic pollutants, primarily sulfuric acid (H₂SO₄) and nitric acid (HNO₃). It results from emissions of sulfur dioxide (SO₂) and nitrogen oxides (NOₓ), which react with water, oxygen, and other chemicals in the atmosphere. Acid rain affects ecosystems, human health, and even man-made structures. In this article, we will explore acid rain in detail—how it forms, its devastating effects, and what we can do to prevent it. Causes of Acid Rain Acid rain originates from both natural sources and human activities . However, human activities contribute the most to this environmental problem. 1. Human ...

  1. Introduction to Acids and Bases Imagine you take a bite of a lemon and feel that sharp, sour taste on your tongue. That sourness comes from citric acid. Now, think about soap—when you touch it, it feels slippery. That’s because soap is made from a base. Acids and bases are everywhere around us, from the food we eat to the cleaning products we use. But what exactly are acids and bases? In simple terms: Acids are substances that taste sour, react with metals, and turn blue litmus paper red. Bases are substances that taste bitter, feel slippery, and turn red litmus paper blue. Scientists have created different definitions of acids and bases to explain their behavior. Let’s explore them in detail. 2. Early Theories of Acids and Bases Scientists have proposed different theories to explain acids and bases. The three most important theories are: a. Arrhenius Theory (1884) Swedish scientist Svante Arrhenius gave one of the first definitions of acids and bases: Acid...

  Exercise: Tick (✓) the Correct Answer (i) The following reaction is an exothermic reaction: H2 + Cl2 = 2HCl (a) By collisions between the molecules (b) From sunlight (c) From the surrounding (d) By collisions of the molecules with the walls of the container Answer: (b) From sunlight Explanation: This is a photochemical reaction , meaning light energy (from sunlight) initiates bond breaking in H₂ and Cl₂ , leading to HCl formation. (ii) Which of the following reactions has the least value of activation energy? (a) H₂(g) + ½ O₂(g) → H₂O(g) (b) C₆₀(s) + O₂(g) → CO₂(g) (c) NaCl(aq) + AgNO₃(aq) → AgCl(s) + NaNO₃(aq) (d) H₂(g) + I₂(g) → 2HI(g) Answer: (a) H₂(g) + ½ O₂(g) → H₂O(g) Explanation: Combustion reactions typically have low activation energy and are highly exothermic . The reaction between hydrogen and oxygen to form water releases significant energy and has low activation energy . (iii) Formation of which hydrogen halide from the elements is an end...