How many moles are 5.42 x 1026 atoms of calcium?

You are making a solution of calcium chloride dissolved in water. you add solid, stir, and it dissolves. you add just a spatula tip full, stir, and the solid does not dissolve. how could you describe the solutions before and after adding the spatula tip amount

Is 343 in the sequence -5, -2, 1, 4, 7

Why is it that 85.48 rounded to two significant figures is 85 and not 86?