1. To determine which two elements react vigorously with each other, we need to consider their positions in the periodic table. Chlorine (Cl) and potassium (K) are in the same group (Group 17 or Group 1, depending on the periodic table used), and elements in the same group generally have similar reactivity. Chlorine is a highly reactive non-metal, and potassium is an extremely reactive metal. Therefore, option B (Chlorine and potassium) is the correct answer.
2. Electronegativity is the tendency of an atom to attract electrons towards itself in a chemical bond. To determine which statement about electronegativity is correct, we need to consider the trends in electronegativity across the periodic table. Electronegativity generally increases across a period from left to right due to increased nuclear charge and decreasing atomic size. Therefore, option A (Electronegativity decreases across a period) is incorrect. The correct answer is option B (Electronegativity increases down a group) since electronegativity generally decreases as you move down a group due to increased atomic size and shielding effects.
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4. To determine the correct statement for a periodic trend, we need to consider the periodic trends involved. Ionization energy is the energy required to remove an electron from an atom. Ionization energy generally increases across a period due to increased nuclear charge and decreased atomic size. Therefore, option A (Ionization energy increases from Li to Cs) is correct. Option B (Melting point increase from Li to Cs) is incorrect because melting point generally decreases down a group due to increased atomic size and metallic bonding. Option C (Ionization energy increases from F to I) is incorrect because ionization energy generally decreases down a group due to increased atomic size and shielding effects. Option D (Melting point increase from F to I) is also incorrect for the same reasons as option B.
5. To determine which compound of an element in period 3 reacts with water to form a solution with a pH greater than 7, we need to consider the properties of the compounds. SiO2 (option A) is a covalent compound and does not react with water to form a basic solution. SiCl4 (option B) is also a covalent compound and does not react with water to form a basic solution. NaCl (option C) is a salt and dissociates in water to form a neutral solution. Na2O (option D) is a metal oxide and reacts with water to form a basic solution, making the pH greater than 7. Therefore, option D (Na2O) is the correct answer.
6. To determine the correct order of atomic radius for Na, K, and Mg, we need to consider their positions in the periodic table. Atomic radius generally increases as you move down a group due to increased atomic size and electron shielding effects. Therefore, the correct order from smallest to largest atomic radius is Mg, Na, K. So, option D (Mg, Na, K) is the correct answer.
Overall, your answers for questions 1, 2, 4, 5, and 6 are correct based on the explanations provided.