How many molecules of sucrose in 0.5 L of a one molar solution of sucrose?

A 1.0 molar solution would be made up by dissolving the the molecular weight of glucose (in grams) in one litre.

The molecular weight of glucose is 180.1559g; so a 1.0M solution would be 180.1559g in 1 litre.

A 0.5M solution would be half that strong, so that would need 90.0780g in 1 litre.

For 500ml you'd need take half the weight into half the volume, so that would be 45.0390g dissolved in water and made up to 500ml.