From 200 mg of CO₂ ,10²¹ molecules are removed.How many moles of CO₂ are left ?

a) 0.288 b) 2.88 c) 0.00288 d) 0.0288

Molar mass of CO₂ = 44 g

Given mass = 200 mg = 0.2 g

No. of moles = 0.2 / 44 = 1 / 220

No. of moles = No . of molecules / Avagadro 's constant

1 / 220 = No. of molecules / 6.022 * 10²³

6.022 * 10²³ / 220 = No. of molecules

= 2.73* 10²¹ Molecules

Now from this 10²¹ molecules are removed 

2.73 * 10²¹ - 10²¹

1.73 * 10²¹  Molecules are now left

No. of moles = Molecules / avogadro's constant

= (1.73 * 10²¹) / (6.022 * 10²³)

= 0.00288  moles

Best of luck

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