Articulation of the letter C and combined CH

We generally pronounce C  as K  in words like   cat, cut, cake cab, can, cap etc and S  in words like city, cite, cent, certain, ice etc

We have rules for this consonant letter.

>> When the letter C comes before A, O, and U, it generally takes sound of K

>>When C comes before E, I and Y, it takes sound of S

There is word Circus which is pronounced sirkus (सर्कस)

>> When C comes with L, It takes Sound of K

As in Clock, Clavichord etc.

>> When C is preceded by vowels it  generally takes sound of K

Example

Doctor(doktur डॉक्टर)

Secret( sikrit or sikrət सीक्रिट)

Vacuum (vækyum वैक्यूम)

>>When C is followed by T, it  takes sound of K

Example

Act (ækt ऐक्ट)

Elect(ɪlɛkt इलेक्ट)

>> The letter C is silent before K  and after S as Check, Ascend, Ascent,Descend, Descent, Fascinate, Fascination, florescent, Obscene, Scene, Scenario, Scent

There is a case in which C comes with H and again combined CH has three different sounds. It is K in words like chasm (kæzəm कैज़म) S in words like cache (kæʃ कैश), and   tʃ (च) words like chalk( tʃɑk चॉक).

There is no specific rules for CH. so it is advisable to go to the dictionary and find the word and learn it pronunciation. But I can give a loose hint for it. The words with Greek origin are pronounced K  for CH  the words are closely linked. Below I am giving you list of words

Ache, Alchemy, Anarchy, Anchor, Arachnid, Archeology, Archaic, Archaism, Archangel, Archtype, Archipelago, Architect, Archive, Bronchi, Chameleon, Chamomile, Character, Charisma, Chasm, Chemical, Chiaroscuro, Chimaera (Chimera), Chiropody, Chiropractor, Choloform, Cholorophyll, Choir, Cholera, Cholesterol, Chord, Choreography, Chris, Chrome, Chronic, Chronology, Chrysanthemum, Cinchona, Clavichord, Cochlea, Conch, Czech, Dachshund, Dichotomy, Drachma, Echo, Epoch, Eucharist, Eunuch, Hypochondria, Inchoate, Lachrymal, Leprechaun, Lichen, Mach, Machination, Masochist, Matriarch, Mechanic, Melancholic, Monarch, Ochre, ogliarch, Orchestra, Orchid, Parochial, Paschal, Psyche, Saccharin,  Schedule (in U.S.A.), Scheme, Scherzo, Schism, Schizoid, Schizophrenia, Scholar, School, Schooner, Sepulchre/ Sepulcher, Stomach, Strychnine, Synchronise, Tech, Trachea, Zucchini.

These above listed words are from Greek, German and Italian origin. 

In the following words CH takes S sound

 Chef, Champagne, Chalet, Charade, Machine, Brochure, Parachute, Chute

These words have origin in modern French language.

When Ch as  tʃ (च) sound

Birch, Breach, Catch, Church, Clutch, Crutch, Couch, Fetch, Hatch,Kitchen, Lunch, Much,  Notch, Peach, Porch, Pooch, Ranch,  Scotch, Snatch, Snitch, Stretch, Starch, Satchel, witch

There is one specific condition that we can notice that CH  is preceded by T, the combined letters are pronounced tʃ (च). These words are having Germanic or old English origin.

Blend Consonant CR gives it  kr(क्र) sound in words.

Example: crow, create, crook etc.