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When two elements combine with each other to form compounds, they do so by exchanging their valencies or combining powers. From the question, Z has a combining power of 3, therefore any element it will combine with among the options must have its valency swapped with that of Z. Among the options, only option C is correct because Oxygen has a valency of 2 while Z has valency of 3. As they combine, Z takes the valency of Oxygen which is 2 while Oxygen takes the valency of Z which is 3.

Electrovalent compounds(ionic) are formed by transfer of electron from metals to non-metals. Thus they are held together by strong electrostatic forces which results to their high melting points. The correct option is C

Ionic bonding involves transfer of electron(s) from metals (potassium) to non-metals(Oxygen). Two atoms of K will combine with one atom of Oxygen to satisfy the electron transfer, thereby fulfilling the octet rule. Option A is the correct answer.

The Nitrogen atom in Ammonia, NH3 has a lone pair of electron which is given out or shared with the Hydrogen ion to form NH4+. Recall that coordinate covalent bond usually involves one of the two participating atoms or molecules donating the lone pair of electrons to be shared by the two atoms or molecules to bond. Therefore option C is the correct answer as ammonium ion is formed by dative bonding or coordinate-covalent bonding.

The electrostatic force of attraction is greatest depending on their strength of electronegativity. In other words, Fluorine atom has the highest electronegativity as it is the most reactive non-metal. The electrostatic force of attraction is greatest between Na and F. The correct answer is option C.

The most reactive non-metals are the Group VII elements (Halogens). Chlorine is the only group VII element among the option, thus it is the most reactive non-metal. The correct answer is option B.

The correct answer is option D. This is because alpha particles, beta particles and gamma rays cannot penetrate a lead box to cause further radioactivity.

CCl4 has no lone pairs on the central carbon atom and is therefore of tetrahedral geometry. Option B is the correct answer.

As water begins to boil, bubbles are formed, thereby increasing the entropy. i.e the degree of disorderliness in the system increases. The correct answer is option B

Using the ideal gas equation, PV = nRT. where \(n = \frac{mass}{\text{molar mass}}\). For Hydrogen, \(\frac{m_H}{M_H} = \frac{PV}{RT}\). For element X, \(\frac{m_X}{M_X} = \frac{PV}{RT}\) Under the same conditions implies \(\frac{PV}{RT}\) is the same for both hydrogen and X. \(\frac{m_H}{M_H} = \frac{m_X}{M_X}\) Molar mass of X = \(\frac{\text{molar mass of hydrogen} \times \text{mass of X}}{\text{mass of hydrogen}}\) = \(\frac{2 \times 9.6}{0.3}\) = 64 g/mol

CO2 (carbon dioxide) is a colorless and odourless gas and very soluble in KOH owning that it is an acidic gas.

Whenever Acids react with carbonate salts to produce carbon(iv) oxide (CO2), water, and a salt: Acid + carbonate → salt + water + carbon(iv) oxide. In other words whenever ac acid reacts with a carbonate salt, CO2 gas is always given off or liberated. The correct answer is option C

When an acid reacts with a metal,Magnesium ribbon, there is an effervescence of hydrogen gas, H2.

No expanded working has been attached for this question yet. The verified answer is Option A.

When potassium oxide (K2O) reacts with water (H2O), it produces potassium hydroxide (KOH): Chemical equation: K2O + H2O → 2KOH The reaction produces a hydroxide compound because the potassium ion balances the hydroxide ion and the solution is alkaline because of the high level of hydroxide ions, which gives it a high pH. Therefore, the correct answer is option D