The relative molecular mass of this hydrocarbon was found by mass spectrometry to be 78. Work out its molecular mass (H=1; C=12)

Which of the following is an indication that a substance has undergone a chemical change? a. no new product has been formed. b. the color of the substance has not changed. c. the original constitute has not changed. d. the molecular structure has changed.

According to the passage, which of these is true about gray water systems? a) gray water systems use plants that require less water. eliminate b) gray water systems require the use of less fossil fuels. c) gray water systems reduce the amount of fresh water used. d) gray water systems reduce the amount water used by shower heads.

Dona wrote the characteristics of two types of galaxies as shown below: type a: has a large flattened core type b: does not have a regular shape which statement is correct? type a is an irregular galaxy and type b is a lens galaxy. type a is a lens galaxy and type b is an irregular galaxy. type a is a spiral galaxy and type b is an elliptical galaxy. type a is an elliptical galaxy and type b is a spiral galaxy.