Q1: The number of water molecules present in a drop of water weighing 0.018 gm is 6.023 x __________

ANS:C - 10²⁰

To find the number of water molecules in a given mass of water, we can use the concept of molar mass and Avogadro's number. The molar mass of water (𝐻2𝑂H2​O) is approximately 18 grams per mole (1 oxygen atom with a molar mass of approximately 16 g/mol and 2 hydrogen atoms with a combined molar mass of approximately 2 g/mol). Given that the drop of water weighs 0.018 grams, we can find the number of moles of water using the formula: Number of moles=MassMolar massNumber of moles=Molar massMass​ Number of moles=0.018 g18 g/mol=0.001 molNumber of moles=18g/mol0.018g​=0.001mol Now, to find the number of water molecules, we can use Avogadro's number, which is approximately 6.023×10236.023×1023 molecules per mole. Number of water molecules=Number of moles×Avogadro’s numberNumber of water molecules=Number of moles×Avogadro’s number Number of water molecules=0.001 mol×6.023×1023 molecules/molNumber of water molecules=0.001mol×6.023×1023molecules/mol Number of water molecules=6.023×1020Number of water molecules=6.023×1020 So, the correct answer is: 6.023×10206.023×1020 Therefore, the option "1020" is the closest match to 6.023×10206.023×1020.