In any ac circuit, is the applied instantaneous voltage equal to the algebraic sum of the instantaneous voltages across the series elements of the circuit? Is the same true for rms voltage?

Explanation

Yes, `v = v_(R ) + v_(L ) + v_(C ) `holds good for instantaneous values.
For rms voltage,
`V_(rms) cancel( = ) ( V_(rms) )_(R ) + ( V_(rms))_(L) + ( V_(rms))_(C )`
because voltage across different elements are not in same phase.