The luminous dials watches are usually made by mixing a zinc sulphide phosphor with an \[\alpha \]- particle emitter. The mass of radium (mass number 226, half-life 1620 years) that is needed to produce an average of 10 \[\alpha \]-particles per second for this purpose is

• A. \[2.77\text{ }mg\]
• B. \[2.77\text{ }g\]
• C. \[2.77\times {{10}^{-23}}g\]
• D. \[2.77\times {{10}^{-13}}kg\]