Which substance has vibrating particles in regular fixed positions

Needthe meter is the standard unit for: 1) height 2) length 3) weight 4) mass

Achemistry student weighs out 0.306 g of citric acid (h3c6h5o7), a triprotic acid, into a 250 ml volumetric flask and dilutes to the mark with distilled water. he plans to titrate the acid with 0.1000 m naoh solution. calculate the volume of naoh solution the student will need to add to reach the final equivalence point. be sure your answer has the correct number of significant digits.

What causes the appearance of lines in a emission spectrum