What is the condition for the first order diffracted beam, in the optical grating?

• A. a tan‚âà√≠¬¨¬±=‚âà√≠¬¨‚Ñ¢
• B. a sin‚âà√≠¬¨¬±=2‚âà√≠¬¨‚Ñ¢
• C. a sin‚âà√≠¬¨¬±=‚âà√≠¬¨‚Ñ¢
• D. a sin‚âà√≠¬¨¬±=3‚âà√≠¬¨‚Ñ¢