-But I heard that 5V zener diode (in reverse) will pass above 5V (it will ground above 5-9V in 9V supply), then how i can connect it at series of 9V supply? Shouldn't i have to connect zener to ground?
There is a 5.1V zener diode available but not a 5.0V zener diode.
It is fed a positive voltage through a series current-limiting resistor and holds the voltage across it to 5.1VDC. Its anode connects to 0V and the positive side of the circuit that it powers and the 1k resistor that feeds it connect to its cathode.
With a 9V supply the zener diode conducts (9V - 5.1V)/1k= 3.9mA to ground. If its load draws more than 3.9mA then the voltage drops to less than 5.1V. If the input voltage to the 1k resistor that feeds it drops then the zener diode current drops. When its current is close to zero then it fails to regulate the voltage.
My oscillator draws about 10mA so the 1k resistor feeding the zener diode has a value that is much too high. if the resistor value is reduced so the zener diode regulates properly then the zener diode will waste a lot of battery power.
Can i use 10MHz crystal for 100MHz? How can I tune the desired frequency?
You cannot tune a crystal oscillator. Here in North America digital FM radios tune in only 99.7MHz, 99.9MHz, 100.1MHz, 100.3MHz and other odd frequencies. These radios do not tune in 100.0MHz which is an even frequency. I don't know what frequencies are used in your country because some countries use even frequencies.
The Rohm BH1415 to BH1417 FM stereo transmitter ICs used a crystal-controlled frequency synthesizer circuit where you could select one of 8 frequencies with a switch. The frequency was crystal-controlled so it was very stable.
You might learn about radio circuits and crystal oscillators some day.
A crystal oscillator without a resonant LC circuit produces a square wave output. A square wave has only odd (not even) harmonics like 3 times, 5 times or 7 times the fundamental frequency. The article says its oscillator produces 5X which is 5 times. Another transistor doubles the frequency (2X). Then the output frequency is 5 x 2= 10 times the crystal frequency.
There, any VHF transistor will work fine?
Any general purpose transistor like a 2N2222 or 2N3904 will work fine as a VHF oscillator.